Operation 123 takes 3.25 hours to complete, and is released at 2:00. Operation 456 takes 2 hours to complete, and is released at 2:01. Both operations require resource ABC. Resource ABC has 3 hours of remaining on-shift time, and the Must Complete option is enabled. Therefore, Operation 123 does not allocate the resource and instead enters a request in the resource's request queue. Operation 456 will allocate the resource because it can be completed within the available time. If you had defined the Maximum Overrun for .25 hours, Operation 123 would have allocated the resource, because the resource would have worked the extra .25 hours to complete the operation. The Allow Overrun option must be enabled on the shift record for Maximum Overrun to function.