diff --git a/calendar/export_execute.php b/calendar/export_execute.php
index 6e76e331867..b4afb2c7076 100644
--- a/calendar/export_execute.php
+++ b/calendar/export_execute.php
@@ -91,7 +91,10 @@ if(!empty($what) && !empty($time)) {
                     list($startmonth, $startyear) = calendar_add_month($startmonth, $startyear);
                     $startmonthday = find_day_in_month(1, $startweekday, $startmonth, $startyear);
                 }
-                $timestart = make_timestamp($startyear, $startmonth, $startmonthday);
+                $gregoriandate = $calendartype->convert_to_gregorian($startyear, $startmonth, $startmonthday);
+                $timestart = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
+                    $gregoriandate['hour'], $gregoriandate['minute']);
+
                 $endmonthday = $startmonthday + $numberofdaysinweek;
                 $endmonth = $startmonth;
                 $endyear = $startyear;
@@ -99,7 +102,9 @@ if(!empty($what) && !empty($time)) {
                     list($endmonth, $endyear) = calendar_add_month($endmonth, $endyear);
                     $endmonthday = find_day_in_month(1, $startweekday, $endmonth, $endyear);
                 }
-                $timeend = make_timestamp($endyear, $endmonth, $endmonthday) - 1;
+                $gregoriandate = $calendartype->convert_to_gregorian($endyear, $endmonth, $endmonthday);
+                $timeend = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
+                    $gregoriandate['hour'], $gregoriandate['minute']);
             break;
             case 'weeknext':
                 $startweekday = calendar_get_starting_weekday();
@@ -110,7 +115,10 @@ if(!empty($what) && !empty($time)) {
                     list($startmonth, $startyear) = calendar_add_month($startmonth, $startyear);
                     $startmonthday = find_day_in_month(1, $startweekday, $startmonth, $startyear);
                 }
-                $timestart = make_timestamp($startyear, $startmonth, $startmonthday);
+                $gregoriandate = $calendartype->convert_to_gregorian($startyear, $startmonth, $startmonthday);
+                $timestart = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
+                    $gregoriandate['hour'], $gregoriandate['minute']);
+
                 $endmonthday = $startmonthday + $numberofdaysinweek;
                 $endmonth = $startmonth;
                 $endyear = $startyear;
@@ -118,15 +126,17 @@ if(!empty($what) && !empty($time)) {
                     list($endmonth, $endyear) = calendar_add_month($endmonth, $endyear);
                     $endmonthday = find_day_in_month(1, $startweekday, $endmonth, $endyear);
                 }
-                $timeend = make_timestamp($endyear, $endmonth, $endmonthday) - 1;
+                $gregoriandate = $calendartype->convert_to_gregorian($endyear, $endmonth, $endmonthday);
+                $timeend = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
+                    $gregoriandate['hour'], $gregoriandate['minute']);
             break;
             case 'monthnow':
                 // Convert to gregorian.
                 $gregoriandate = $calendartype->convert_to_gregorian($now['year'], $now['mon'], 1);
 
-                $timestart = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day']);
-                $timeend = make_timestamp($gregoriandate['year'], $gregoriandate['month'],
-                    calendar_days_in_month($now['mon'], $now['year']), 23, 59, 59);
+                $timestart = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
+                    $gregoriandate['hour'], $gregoriandate['minute']);
+                $timeend = $timestart + (calendar_days_in_month($now['mon'], $now['year']) * DAYSECS);
             break;
             case 'monthnext':
                 // Get the next month for this calendar.
@@ -136,9 +146,9 @@ if(!empty($what) && !empty($time)) {
                 $gregoriandate = $calendartype->convert_to_gregorian($nextyear, $nextmonth, 1);
 
                 // Create the timestamps.
-                $timestart = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day']);
-                $timeend   = make_timestamp($gregoriandate['year'], $gregoriandate['month'],
-                    calendar_days_in_month($nextmonth, $nextyear), 23, 59, 59);
+                $timestart = make_timestamp($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
+                    $gregoriandate['hour'], $gregoriandate['minute']);
+                $timeend = $timestart + (calendar_days_in_month($nextmonth, $nextyear) * DAYSECS);
             break;
             case 'recentupcoming':
                 //Events in the last 5 or next 60 days
diff --git a/calendar/lib.php b/calendar/lib.php
index a805f33b279..6c7bf6e59c7 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -227,10 +227,10 @@ function calendar_get_mini($courses, $groups, $users, $calmonth = false, $calyea
 
     list($d, $m, $y) = array($date['mday'], $date['mon'], $date['year']); // This is what we want to display.
 
-    // Get Gregorian date.
+    // Get Gregorian date for the start of the month.
     $gregoriandate = $calendartype->convert_to_gregorian($date['year'], $date['mon'], 1);
 
-    // Store the gregorian year and month to be used later.
+    // Store the gregorian date values to be used later.
     list($gy, $gm, $gd, $gh, $gmin) = array($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
         $gregoriandate['hour'], $gregoriandate['minute']);
 
@@ -249,7 +249,7 @@ function calendar_get_mini($courses, $groups, $users, $calmonth = false, $calyea
 
     // These are used for DB queries, so we want unixtime, so we need to use Gregorian dates.
     $display->tstart = make_timestamp($gy, $gm, $gd, $gh, $gmin, 0);
-    $display->tend = make_timestamp($gy, $gm, $display->maxdays, 23, 59, 59);
+    $display->tend = $display->tstart + ($display->maxdays * DAYSECS) - 1;
 
     // Align the starting weekday to fall in our display range
     // This is simple, not foolproof.
@@ -860,12 +860,14 @@ function calendar_top_controls($type, $data) {
     // We need to get the previous and next months in certain cases.
     if ($type == 'frontpage' || $type == 'course' || $type == 'month') {
         $prevmonth = calendar_sub_month($date['mon'], $date['year']);
-        $prevmonthtime = $calendartype->convert_to_gregorian($prevmonth[1], $prevmonth[0], $date['mday']);
-        $prevmonthtime = make_timestamp($prevmonthtime['year'], $prevmonthtime['month'], $prevmonthtime['day']);
+        $prevmonthtime = $calendartype->convert_to_gregorian($prevmonth[1], $prevmonth[0], 1);
+        $prevmonthtime = make_timestamp($prevmonthtime['year'], $prevmonthtime['month'], $prevmonthtime['day'],
+            $prevmonthtime['hour'], $prevmonthtime['minute']);
 
         $nextmonth = calendar_add_month($date['mon'], $date['year']);
-        $nextmonthtime = $calendartype->convert_to_gregorian($nextmonth[1], $nextmonth[0], $date['mday']);
-        $nextmonthtime = make_timestamp($nextmonthtime['year'], $nextmonthtime['month'], $nextmonthtime['day']);
+        $nextmonthtime = $calendartype->convert_to_gregorian($nextmonth[1], $nextmonth[0], 1);
+        $nextmonthtime = make_timestamp($nextmonthtime['year'], $nextmonthtime['month'], $nextmonthtime['day'],
+            $nextmonthtime['hour'], $nextmonthtime['minute']);
     }
 
     switch ($type) {
diff --git a/calendar/renderer.php b/calendar/renderer.php
index efb4725baf9..fd9b99eeb55 100644
--- a/calendar/renderer.php
+++ b/calendar/renderer.php
@@ -172,12 +172,14 @@ class core_calendar_renderer extends plugin_renderer_base {
         $date = $calendartype->timestamp_to_date_array($calendar->time);
 
         $prevmonth = calendar_sub_month($date['mon'], $date['year']);
-        $prevmonthtime = $calendartype->convert_to_gregorian($prevmonth[1], $prevmonth[0], $date['mday']);
-        $prevmonthtime = make_timestamp($prevmonthtime['year'], $prevmonthtime['month'], $prevmonthtime['day']);
+        $prevmonthtime = $calendartype->convert_to_gregorian($prevmonth[1], $prevmonth[0], 1);
+        $prevmonthtime = make_timestamp($prevmonthtime['year'], $prevmonthtime['month'], $prevmonthtime['day'],
+            $prevmonthtime['hour'], $prevmonthtime['minute']);
 
         $nextmonth = calendar_add_month($date['mon'], $date['year']);
-        $nextmonthtime = $calendartype->convert_to_gregorian($nextmonth[1], $nextmonth[0], $date['mday']);
-        $nextmonthtime = make_timestamp($nextmonthtime['year'], $nextmonthtime['month'], $nextmonthtime['day']);
+        $nextmonthtime = $calendartype->convert_to_gregorian($nextmonth[1], $nextmonth[0], 1);
+        $nextmonthtime = make_timestamp($nextmonthtime['year'], $nextmonthtime['month'], $nextmonthtime['day'],
+            $nextmonthtime['hour'], $nextmonthtime['minute']);
 
         $content  = html_writer::start_tag('div', array('class' => 'minicalendarblock'));
         $content .= calendar_get_mini($calendar->courses, $calendar->groups, $calendar->users, false, false, 'display', $calendar->courseid, $prevmonthtime);
@@ -417,10 +419,9 @@ class core_calendar_renderer extends plugin_renderer_base {
             $calendar->time = time();
         }
 
-        // Get Gregorian date.
+        // Get Gregorian date for the start of the month.
         $gregoriandate = $calendartype->convert_to_gregorian($date['year'], $date['mon'], 1);
-
-        // Store the gregorian year and month to be used later.
+        // Store the gregorian date values to be used later.
         list($gy, $gm, $gd, $gh, $gmin) = array($gregoriandate['year'], $gregoriandate['month'], $gregoriandate['day'],
             $gregoriandate['hour'], $gregoriandate['minute']);
 
@@ -437,7 +438,7 @@ class core_calendar_renderer extends plugin_renderer_base {
 
         // These are used for DB queries, so we want unixtime, so we need to use Gregorian dates.
         $display->tstart = make_timestamp($gy, $gm, $gd, $gh, $gmin, 0);
-        $display->tend = make_timestamp($gy, $gm, $display->maxdays, 23, 59, 59);
+        $display->tend = $display->tstart + ($display->maxdays * DAYSECS) - 1;
 
         // Align the starting weekday to fall in our display range
         // This is simple, not foolproof.