Service stops responding after adding blocked once off timing

After selecting the Exclude this time period on the selected days... under Schedules (with Start time 00:00:00, End time 23:59:59 and all Exclusion days selected) the CPU reached 100% usage and the interface stopped responding. This only seems to happen when the time is first created or the service is restarting. After a long period, the interface responds again and correctly displays that the timing should never run. Subsequent attempts to view the next run do not slow down.