It will automatically speed to a certain number EX: 25, 20, 15 on the play clock, the seconds on the game clock will also reflect accordingly.
EX: 5:00 game clock and a 40 sec play clock will equal 4:35 game clock and 15 on the play clock, if you choose to set the accelerated clock to go to 15, as you break the huddle.
It wont affect your gameplay.