I had this one happen today. U17 girls match with 30 minute halves. The event is designed for college coaches to scout players, so this is much more about managing a game to give the players a chance to show their skills. Games are to start every 75 minutes on a full-sized indoor field, so we are playing essentially zero added time.
Team Light Blue's keeper receives a pass from a defender just as my watch hits 30:00 and my Garmin app buzzes. I'm thinking to myself, "As soon as the keeper boots the ball upfield about 30 yards or passes wide to one of her outside backs, I'll blow the whistle for half." Keeper hits the ball on the ground right in the path of Team Dark Blue's striker who basically deflects the ball into the net.
All I can say is that it was a good thing I didn't blow the whistle as the keeper played the ball, as that would have presented a host of issues!