It means that it normally checks whether the opponent has moved every 7.5 seconds, but when tighter time controls are set, it will check at smaller intervals, ranging from every 4 seconds to every half second, depending upon how quickly the game is supposed to go.
It means that it normally checks whether the opponent has moved every 7.5 seconds, but when tighter time controls are set, it will check at smaller intervals, ranging from every 4 seconds to every half second, depending upon how quickly the game is supposed to go.