Is there a way to block i.e.: twitter or facebook iOS apps during specified times? i.e.; 8am - 4pm? Obviously they can use them after hours, and we can block them from logging in via safari, but don't want to restrict the app entirely from their iOS devices.
You would have to block access to the service via some sort of internet filter. There isn't any mechanism to block apps (let alone by time) in iOS. Other than putting the iOS device in single app mode, which isn't what you're looking for.
We are just in a trial with the Umbrella service and are very impressed:
you can filter Internet access and it doesn't matter if the device is in school, at home or on the road. Administration is rather simple over a web admin interface.