Same here guys, about 20 minutes before the body makes the transition to cycling mode. It really takes a good 45 minutes before I'm ready to climb telephone poles.
The hotter and more humid the better.

Hills: I Use 48/36/26 and 27/13 and take advantage of the available higher cadence, lower KW output configs if faced with hills during early parts. I see no reason to look at the upcoming grade and say "why am I doing this?", but been there done that. Altering/playing with different pedaling techniques seems valuable.
(I really avoid going into the red til the last half hour.)

Mini-intervals seem to be crucial after the first 20 min, increasing intensity and duration according to comfort. I used to do 25-40 dailys but now do more spirited 1 hour, 15-20 mi rides with rare daily breaks and for some reason feel Like I'm in better shape now than ever. Don't now why.

I never go out with the intention of excercise, but for fun. Exercise, however, typically follows.

Lastly, I road much in my youth, rather mindlessly. I started back in '04 and have found that there's no substitute for experience: '04 vs now. Pacing, gearing, just plain feel, safety, many subtleties of what is really an art form Undergo radical changes.

A few thoughts from one still on the vast learning curve.
Dave