Warm warm water hotter then warm though. No oils and just relax b4 the shower u should have rough sex. sorry 4 tmi. but this worked for me rough sex,hot bath flash dance,jumping jacks,squats.
At this point in your pregnancy you'll be fine. Anything that helps the pain and relax you. You'll be fine to use oils etc, but obviously if you're in labour and your waters break, oils won't be a good idea.
I dont think it matters how long you are in the bath. The difference between a bath and hot tub is that the bath water will cool down where as hot tub water says at a consistent temperature. I have still continued to use the hot tub though I just turn it down to 100 as that was what my dr said was ok. As for oils I am sure its fine to use them.. maybe dont do a bath once your water breaks though.