So there's a 'Tour of Richmond' on Oct 5th here in VA that I want to prep for. I'm not trying to get 1st place, but I want to use this event to give me a goal to shoot for, meaning I want to be able to do 60 miles without collapsing. In the 6 years of owning a road bike, I'm lucky to get 500 miles a year. With a family (2 and 4yr old), it's very difficult to get the saddle time I need while keeping the peace at home. I always feel guilty when I'm out for 3 hours while my wife is home with the kids. I work 40hrs a week and she's part-time, so she's with the kids a LOT more than I am. Having said that, I can comfortably be on the saddle for a total of about 6 hours a week.
Something like:
Tuesday: 12 miles
Thursday: 30 miles
Saturday: 40 miles

I can add 45min of gym cardio as well. Given this info, do you think it's enough training to comfortably do a 60 mile ride without too much fatigue? I hope this isn't too general of a question.