Can't answer the question on spread time, but I was on an extremely fast track to IGRT, and they did say that they had to wait NO LESS THAN 18 weeks regardless. That is, at least for my surgeon, the estimated minimum internal healing time. Since we talk about
RT stopping recovery of continence, it would be better to say healing in general.
It was described to me that radiation disrupts normal healing, and may make it very difficult or impossible (thus the association to incontinence). I can see that from some old colo-rectal issues. In the past they would come and go in a few days. Now they come and stay.
I was actually 25 weeks out on day 1 of radiation (we started prep work about 4 weeks before that).
So, if your surgeon follows the same school of thought, it will be a while before they would start radiation.
Gives you something to consider when they tell us little or no lifting, no strains, no heavy exercise for weeks / months after surgery. Here they are following their own advice, even if a lot of us seem to want to be back out at yard work or in the gym a week later.