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.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.