diff --git a/plugins/calendar/calendar_ui.js b/plugins/calendar/calendar_ui.js
--- a/plugins/calendar/calendar_ui.js
+++ b/plugins/calendar/calendar_ui.js
@@ -1709,20 +1709,23 @@
         eventstart = clone_date(event.start, event.allDay ? 1 : 0).getTime(),  // calculate with integers
         eventend = clone_date(event.end, event.allDay ? 2 : 0).getTime(),
         duration = eventend - eventstart - (event.allDay ? HOUR_MS : 0),  /* make sure we don't cross day borders on DST change */
-        sinterval = freebusy_data.interval * 60000,
+        sinterval = freebusy_data.interval * 60000 / (event.allDay ? 1 : (settings.timeslots || 1)),
         intvlslots = 1,
         numslots = Math.ceil(duration / sinterval),
-        checkdate, slotend, email, ts, slot, slotdate = new Date();
+        fb_start = freebusy_data.start.getTime(),
+        fb_end = freebusy_data.end.getTime(),
+        checkdate, slotend, email, ts, slot, slotdate = new Date(),
+        candidatecount = 0, candidatestart = false, success = false;
 
       // shift event times to next possible slot
       eventstart += sinterval * intvlslots * dir;
       eventend += sinterval * intvlslots * dir;
 
       // iterate through free-busy slots and find candidates
-      var candidatecount = 0, candidatestart = candidateend = success = false;
-      for (slot = dir > 0 ? freebusy_data.start.getTime() : freebusy_data.end.getTime() - sinterval;
-            (dir > 0 && slot < freebusy_data.end.getTime()) || (dir < 0 && slot >= freebusy_data.start.getTime());
-            slot += sinterval * dir) {
+      for (slot = dir > 0 ? fb_start : fb_end - sinterval;
+            (dir > 0 && slot < fb_end) || (dir < 0 && slot >= fb_start);
+            slot += sinterval * dir
+      ) {
         slotdate.setTime(slot);
         // fix slot if just crossed a DST change
         if (event.allDay) {
@@ -1737,7 +1740,7 @@
         // respect workingours setting
         if (freebusy_ui.workinhoursonly) {
           if (is_weekend(slotdate) || (freebusy_data.interval <= 60 && !is_workinghour(slotdate))) {  // skip off-hours
-            candidatestart = candidateend = false;
+            candidatestart = false;
             candidatecount = 0;
             continue;
           }
@@ -1746,11 +1749,15 @@
         if (!candidatestart)
           candidatestart = slot;
 
-        // check freebusy data for all attendees
         ts = date2timestring(slotdate, freebusy_data.interval > 60);
+        // @TODO: freebusy_data slots should use sinterval not full hour
+        if (!event.allDay)
+          ts = ts.replace(/[0-9]{4}$/, '0000');
+
+        // check freebusy data for all attendees
         for (var i=0; i < event_attendees.length; i++) {
           if (freebusy_ui.attendees[i].role != 'OPT-PARTICIPANT' && (email = freebusy_ui.attendees[i].email) && freebusy_data[email] && freebusy_data[email][ts] > 1) {
-            candidatestart = candidateend = false;
+            candidatestart = false;
             break;
           }
         }
@@ -1761,22 +1768,15 @@
           candidatecount = 0;
           continue;
         }
+        else if (dir < 0)
+          candidatestart = slot;
         
-        // set candidate end to slot end time
         candidatecount++;
-        if (dir < 0 && !candidateend)
-          candidateend = slotend;
         
         // if candidate is big enough, this is it!
         if (candidatecount == numslots) {
-          if (dir > 0) {
-            event.start.setTime(candidatestart);
-            event.end.setTime(candidatestart + duration);
-          }
-          else {
-            event.end.setTime(candidateend);
-            event.start.setTime(candidateend - duration);
-          }
+          event.start.setTime(candidatestart);
+          event.end.setTime(candidatestart + duration);
           success = true;
           break;
         }