For bone metastases requiring surgical stabilization, what time interval from the date of surgery do you use for post-op radiation?  

Generally, the surgical stabilization minimizes the capability of short-term catastrophe in (like path fracture), what I presume to be a long bone that has undergone surgical stabilization. I'd probably want to give a few days just to maximize local wound healing but starting sometime, maybe 1-2 wee...

We generally treat the same day as surgery or if not, within 24 hours.