IM Lock Scheduler
With IMLock, you can schedule your blocking.
The way it works, you can create multiple schedules,
which are time periods where blocking takes place.
Wherever the schedule is left blank, no blocking will happen.
In the event there is no schedule, then blocking will
take place all of the time.
You can set scheduling in Android Admin, Web Admin, as well
as Windows Admin.
In the Enterprise version, you can have a seperate
schedule with each group policy.