diff --git a/library/Icinga/Data/Db/DbQuery.php b/library/Icinga/Data/Db/DbQuery.php
index 25acd8905..9a36c6bef 100644
--- a/library/Icinga/Data/Db/DbQuery.php
+++ b/library/Icinga/Data/Db/DbQuery.php
@@ -224,17 +224,17 @@ class DbQuery extends SimpleQuery
 
     protected function valueToTimestamp($value)
     {
-        if (ctype_digit($value)) {
+        if (is_string($value)) {
+            if (ctype_digit($value)) {
+                $value = (int) $value;
+            } else {
+                $value = strtotime($value);
+            }
+        } elseif (! is_int($value)) {
             $value = (int) $value;
-        } elseif (is_string($value)) {
-            $value = strtotime($value);
         }
 
-        if (is_int($value)) {
-            $value = $this->timestampForSql($value);
-        }
-
-        return $value;
+        return $this->timestampForSql($value);
     }
 
     /**
diff --git a/modules/monitoring/application/views/scripts/list/eventgrid.phtml b/modules/monitoring/application/views/scripts/list/eventgrid.phtml
index aafa9b6b1..8809c533e 100644
--- a/modules/monitoring/application/views/scripts/list/eventgrid.phtml
+++ b/modules/monitoring/application/views/scripts/list/eventgrid.phtml
@@ -58,7 +58,7 @@ foreach ($summary as $entry) {
     $caption = sprintf(
         $settings[$column]['tooltip'],
         $value,
-        $this->formatDate(strtotime($day))
+        $this->formatDate(strtotime($day ?? ''))
     );
     $linkFilter = Filter::matchAll(
         Filter::expression('timestamp', '<', strtotime($day . ' 23:59:59')),
diff --git a/modules/monitoring/library/Monitoring/Timeline/TimeRange.php b/modules/monitoring/library/Monitoring/Timeline/TimeRange.php
index 26d72505e..08c7a2c3a 100644
--- a/modules/monitoring/library/Monitoring/Timeline/TimeRange.php
+++ b/modules/monitoring/library/Monitoring/Timeline/TimeRange.php
@@ -119,12 +119,14 @@ class TimeRange implements Iterator
     /**
      * Return whether the given time is within this range of time
      *
-     * @param   int|DateTime    $time   The timestamp or date and time to check
+     * @param   string|int|DateTime    $time   The timestamp or date and time to check
      */
     public function validateTime($time)
     {
         if ($time instanceof DateTime) {
             $dateTime = $time;
+        } elseif (is_string($time)) {
+            $dateTime = DateTime::createFromFormat('d/m/Y g:i A', $time);
         } else {
             $dateTime = new DateTime();
             $dateTime->setTimestamp($time);