Jane,
I'm glad finally have something to post about. I hope we helped. It sound like you made an informed decision, got a good price and went about it the right way. I didn't see where you are located, but this time of year if I was to fill my tub the water out of the spout would be 40 degrees. My tub which has a, I think, a 4.5kh heater, heats at about 4 degrees an hour, so that would be about 15 hours to come to temp. I remember that first day waiting for it to get up to temp. Good luck, I hope you will report back and let us know how that went.
PS, I said 4 degrees an hour, but I've noticed on a cold tub, its less than 4 degrees for the first hour and if the tub is back at 100, and I turn it to 104, it takes less than an hour, but 4 is a good average.