bolo - depends on a lot of things. Ambient temp in room where chiller is, set points (how much are you dropping the temp each time it kicks on? how often is it coming on?), flow through chiller (too slow or too fast of flow can mean the chiller needs to stay on longer to reach your set point), etc, etc.
Basically, w/o knowing a lot more things it's hard to say whether your chiller needs fixing.
For reference, I have a 140 gal with a 1/4 horsepower chiller (Arctica) that stays on for 30 minutes when it comes on to drop my temp.