Time - any way to limit continuous use or have multiple periods?

Has anyone worked out a way to limit continuous use?  What I need, is to stop my child using his whole 2 hour PC time allowance in one session.

What's needed is either a limit on continuous use with an enforced break at the end, or the ability to set individual time limits to periods within the day - e.g., between 9-12, allow 1 hour of use and between 4-7, a further 1 hour.

So far, Norton Support's response to this was to send me the link to the (minimal and not helpful in this case) standard time limit instructions.

Thanks!

Jeff