I would second road warrior. Looks to me you could easily get down to the 70min
range over a few months. After that you would have to start riding with a group
that tends to stretch you a bit, makes you work, and a bit of coaching might help.
Although it is not strictly necessary to ride much more than 25-30mi to train for a
TT, the knowledge you can do 50-75mi and not feel to bad, makes the 25mi TT
seem easier. Circular course tend to neutralize wind more than out and back courses. Steve