I've set a goal to do a sprint triathlon next spring. After looking at recent race results, it looks like the winners in my age category were all pushing about 300W over the cycling portion (20km, 33 minutes).

So that's my goal.

My question is how best to go about getting there. I don't care about being able to ride a century or climb the Alpe d'Huez - I just want to be as competitive as possible over this (apparently by board standards short) distance. Should I focus on regularly riding the actual distance, and gradually bringing up the average speed (and hence power output)? Or should I focus on riding for the actual time, with ever-increasing, ever-lengthening intervals where I'm actually hitting 300W?

Right now, I can do about 120W over the full time period, and based on Strava's analysis, I can hold 300W for about a minute at a time.