Hi @gopher
I had PT-led hydrotherapy after a couple of my hip surgeries. It was after revisions, so many months after surgery. It was just 6 hourly sessions over 3 weeks, and the expectation was for me to continue with the exercises in a local pool (2 or 3 times a week) to get full benefit. I found it to be very beneficial indeed and had hoped to be able to do the same after my last surgery. Not an option yet due to Covid

. A word of caution - it's very easy to do too much in your first session!
There are many on the site who have returned to swimming after surgery. You'll be able to get an idea of how soon they were able to get back in the pool by reading some of their threads. As to when it will be safe for you to do so, something to ask your OS at your post op appointment.
Not long to go now before your first surgery. Good luck!