Hurry I gotcha!!!!
solution:
- first let 1sec & 3sec guy cross the bridge
- 1sec guy comes back and 12sec & 8sec guys crosses the bridge
- 3sec guy comes back & 1sec , 6sec person crosses
- 1sec guy comes back and together 1 & 3 sec crosses the bridge
- u'll have still a sec remaining
sounds confusing

,but worth trying
tictactoe ,thanks for sharing