Bike Training for Oympic Tri

I was wondering if someone could give me some advise on training for a bike race of 25 miles for olympic. How far should I go for a long ride, I have been doing about 60-70 miles every other weekend and been doing rides on the stationary bike for 40-50 minutes monday through friday. Basically I have 8-10 hrs each week to commit to cycling how should I use this time for 6 workouts? During the week I can't ride longer then 90 mins but weekend i can ride longer. Should i do those 2X20 min tempos, and what types of intevals will prepare me best?

elite: 175-225 miles/wk
AG: 125-175 miles/wk
Novice: 75-125

zone 2 40%, zone 3 30%, zone 4 20%, zone 5 10%