Allow temporary increases to time limits

A frequent use case is that the child wants to have "just a little more time" on the phone. Currently I can accoplish this by increasing the daily time limits, but this increases the time limit on future days as well. I also frequently forget to reset the limits back to where they were.

In other words, I would like to be able to give a one-time increase to the time limits that does not alter the basic settings.