Understanding Merge Blackouts
A merge blackout is a predetermined time period in which automatic merges are disabled. A Merge that starts before a merge blackout period will continue until either it completes or until it is canceled, even if the merge continues into a blackout period. If you want to stop any merges at the beginning of a blackout period, you must cancel them manually as described in Canceling a Merge. Because merges that start just before a blackout period will continue into the blackout period, if you want to be sure no merges occur during a time period you should make the blackout period start earlier. This is especially true for merges that might run a long time.
If the system determines that a merge is required and it is during a blackout period, the merge will not begin until the blackout period is past.