I would even say that you can train to race competitively in 8 hours a week. I used to focus on an Eddie B style training of long LSD rides with mid week intervals. Now I am focusing more on the intensity. It certainly can't hurt to do the 90 mile weekend training rides but if time is short then you need alternatives. Most of the cat 4 races I do are 60 miles tops so doing the long marathon rides may not be necessary.
btw I am by far no expert on the topic in fact I am probably offering a worthless opinion but at least this is going to be my approach this year.