Throwing Between Games?

I bought the Tuff Cuff book for my son (17, physicially fit) and he used the in-season workouts and training for a starting pitcher during the high school season. In between starts he would use the 10-minute long toss once or twice, (not on consecutive days), and a 25-35 pitch pen once or twice (depending on the length between starts) For summer ball with a travel team, he has been a starter for some games and called on for relief in other games. Typically his pitch count for relief can range from 10-50 pitches, depending on the situation. Since there are no regular intervals between outings, he is following the Tuff Cuff for Relief pitchers, but is not sure when/how and how often he should throw between games.