How long should I expect until I’m back in the gym?

I got very serious with my health a little over a year ago and picked up personal training/boxing, which combined with a major diet change, I’ve lost about 90lbs. I’ve finally booked for my appt & a little nervous about falling off the wagon/ruining my routine post op. So how long should I reasonably expect to be on the DL and not able to workout?

Most sessions include mixed cardio, weights, stretches, then boxing (bag and pads only).