UPDATE
Just want to let you all know that last night during the 20 minute break from practice, I went to my car in the parking lot, sat in the back seat and played a variety of easy exercises that included long tones, lip slurs and some scales including chromatic scales. I took a good rest between each exercise and figure I played about 12 or 13 minutes of the 20 minute break. When practice resumed I played the remaining 40 minutes of practice without any embouchure problems.
I guess not playing for 20 minutes was encouraging edema. I don't know, but I do know I will be continuing to play during the breaks from now on.