Personally, I am at the field an hour before game time for HS games. I am nervous if I have not seen my partner by 40 min prior and we are having words if he is not there by 30. Of course, I have longer travel times and leave room just in case there is traffic or an unforeseen issue. Getting the teams off the field can be moved along by letting them know to hustle on and off. As for P and C who are on base, THIS is the reason for courtesy runners, not to make up for P or C who is not fleet of foot. The only time I will give a C extra time is if she was the last at bat and needs to get geared up. All Cs in the area I work know me, know what I expect and know they will get 2 pitches to themselves if they needed to gear up, one for the P and one to throw down on IF they hustle. Make it a habit as an umpire and the players will make it a habit to be timely.