I am a teacher and therefore, on my feet typically 5-7 hours of the day. I worked until 6 days before my due date last time (she arrived on her due date!) and plan about the same this time, depending on how things are going.
I also have an on my feet job and I'm 25 weeks now. I plan to work till I'm physically unable- that's what I tell my clients whenever they ask how long I plan on working. Unless my midwife instructs me to stop any sooner, I'll work up till as close to my due date as possible, again as long as I am physically able. Just take breaks and sit every chance you get, even if it's just for 5 minutes.
I have a on your feet job and stayed till i was 38week think its all just personal preferanceas every 1 has a different pregnancy