I shoot for 90 minutes befor the race also. Although, I usually get there earlier than that, escpecially if its a long drive because I build in a liberal allowance for the driving time.

I like to have at least 30 minutes to warm up. So time to park, find registration, get registered, get dressed, pump tires, pin number, etc. and a 45 minute warm up, scout course, I'd be rushed with less than 90 minutes.