diff --git a/fhem/FHEM/90_at.pm b/fhem/FHEM/90_at.pm
index 9fea6ea2b..f043396b4 100755
--- a/fhem/FHEM/90_at.pm
+++ b/fhem/FHEM/90_at.pm
@@ -23,27 +23,22 @@ at_Initialize($)
 }
 
 
-my $at_stt_sec;
-my $at_stt_day;
+my %at_stt;
 my $at_detailFnCalled;
 
 sub
 at_SecondsTillTomorrow($)  # 86400, if tomorrow is no DST change
 {
   my $t = shift;
-  my $day = int($t/86400);
+  my $dayHour = int($t/3600);
 
-  if(!$at_stt_day || $day != $at_stt_day) {
-    my $t = $day*86400+12*3600;
+  if(!$at_stt{$dayHour}) {
     my @l1 = localtime($t);
     my @l2 = localtime($t+86400);
-    $at_stt_sec = 86400+
-                ($l1[2]-$l2[2])*3600+
-                ($l1[1]-$l2[1])*60;
-    $at_stt_day = $day;
+    $at_stt{$dayHour} = 86400+($l1[2]-$l2[2])*3600;
   }
 
-  return $at_stt_sec;
+  return $at_stt{$dayHour};
 }
 
 
@@ -85,7 +80,7 @@ at_Define($$)
   $nt -= ($lt[2]*3600+$lt[1]*60+$lt[0])         # Midnight for absolute time
                         if($rel ne "+");
   $nt += ($hr*3600+$min*60+$sec); # Plus relative time
-  $nt += at_SecondsTillTomorrow($ot) if($ot >= $nt);  # Do it tomorrow...
+  $nt += at_SecondsTillTomorrow($nt) if($ot >= $nt);  # Do it tomorrow...
   @lt = localtime($nt);
   my $ntm = sprintf("%02d:%02d:%02d", $lt[2], $lt[1], $lt[0]);
   if($rep) {    # Setting the number of repetitions