My job was similar to your husband's in that it required weekly travel. I retired just prior to my diagnosis but I think I can say that it will be very difficult to keep up with a heavy travel schedule and do daily RT sessions. I would ask the doctor how much time can be taken between sessions without lessening the effectiveness. He should also consider the side effects such as diarrhea. It starts about
half way through and would be a disaster if he is on a plane when the urge arises. Particularly on take off or landing when you must remain seated. I recall during my treatment thinking that there would be no way to travel while in the midst of it.
Fatigue was not so great during the RT or during the first year of the HT. The second year of HT was worse than the first in this respect. Even so I returned to work for my former employer on a contract basis approximately six months after completing the radiation and while in the middle of the HT. I was lucky in that I had no lingering side effects from the RT as far as being able to work. I did notice that I did not feel as sharp in the mental sense but I do not believe it was noticeable to those for whom I worked. By the way, my work was primarily mental in nature (engineering) but did require me to be on the mill floor a good bit. The fatigue was manageable.
I would wait and see where he stands next week with the PSA. End of February is still out a ways. Even waiting until end of March to begin radiation would likely not be detrimental especially if he starts HT in the interim. Hopefully his numbers will be good and he will not need to start the salvage right away.
Best of luck to both you and your husband.