I haven't tried this app yet, but am looking for a similar feature you're looking for. I think this one would work for you. I'm looking for one I can set a timer for when I give my child my ipad to play on - not a maximum daily time like this one.
TimeLock allows parents to set a daily usage time limit on their child's iPod
https://itunes.apple.com/us/app/timelock-time-limit-for.../id440218332?...
Jun 29, 2011 - Does your child use their iPod/iPad/iPhone too much? Do you want to limit the time they spend on it? TimeLock allows parents to set a daily usage time limit on their child's iPod, ... The timer is reset automatically each day.