In hydrotherapy they use hot/cold therapies for many ailments, but this is strictly hyperthermia, no cold stuff here. I am not sure what herbs you are talking about, abut i used nothing.
THe temp of the bath is about the same as a hot tub. My baths took about 20-25 minutes to get to my body temp 103 degrees once I submerged myslef (not your head though)
I wrapped myself in a queen size sheet and then a warm large blanket as well, making sure you are wrapped up to your neck. You will be sweating at this point, and your heart rate will be elevated. Have the lights dimmed and just relax, take your temp until it reaches normal, and THEN you can slowly unwrap yourself.
You would probably want to rinse in the shower afterwards as you will have sweated and if you have morgs, there should be stuff to rinse off.