You can make a race. Have a 100 long chain of redstone repeaters on the sideline, all set to the longest delay. That is your timer. Have it close the door when it reaches the end, this means the "time ran out." Then make the track of your race full of obstacles.
====================== <--Redstone
<><><><><><><><><><><> <--Glass
XXXXXXXXXXXXXXXXXXXXXX <--Track
XXXXXXXXXXXXXXXXXXXXXX <--Track
XXXXXXXXXXXXXXXXXXXXXX <--Track
XXXXXXXXXXXXXXXXXXXXXX <--Track
<><><><><><><><><><><> <--Glass
