A question was raised recently about how to finish a period early (before the official time has elapsed) if the umpire decides to end it. I hope this post explains how this can be done.
You can end a period early (before the time has naturally expired) by touching and holding the start/pause button while it is in progress. This will give you the choice of whether to continue the period, or to finish it immediately, and set the match up for the next period (or finish the match if it is the last period). So if you set your periods to be the 'official' duration, then if the umpire finishes one early, you do not have to wait for the clock to run down before getting ready to start the next one.