De-activate user group for certain period of time everyday.

I have a website on which users make entries to custom post all day. I want to restrict then to a certain period of time, say about 8 hours a day, and then make their account inactive for rest of the hours.
I want this to be repeated every day.
I tried to search the repository but couldnt find and. Can anyone suggest a plugin that will provide functionality to disable a whole user group for a certain period of time everyday.