Unrestrict app/site for X minutes or until HH:MM, etc.

So we use the Parental Controls to block a number of apps/sites as a general rule, but often my child reasonably needs that site or app for a few minutes (or hours). Currently, I log in and turn off the filter and then set myself a timer to re-block it, but it would be great if there was an "unblock for <amount of time>" or "unblock until <HH:MM>" or something like that so that I didn't have to go back each time to re-enable the block. That would both save a step and avoid the times when I fail to re-block it and find out days later that it has been used/abused.

Thanks!