First of all, congratulations on expanding your practice time, I'm sure you will soon begin to reap the benefits.
One thing that might help you avoid unnecessary fatigue would be to dedicate the first hour or so of your playing day to a consistent daily routine, not just a warm-up (if you don't already do so). I have a routine that doesn't just get me warm, but it also covers low range, finger technique, pronunciation, flexibilities, high range, etc. etc.
The more you can "average out" your practice, the less fatigue you'll probably experience. For example, two hours for five days in a row is better than four days with one hour of practice with six hours of practice on the fifth day.
I wouldn't worry too much about "strengthening the embouchure". Make sure that you're playing with your best sound and a pure airstream always, and the tiny muscles will take care of themselves.
JACE VICKERS, DMA
Assistant Director of Bands
Assistant Professor of Low Brass
East Central University