Who knows! It's such an individual thing. Some people can do it after a couple of weeks and many can do it starting at 6 weeks or a couple of months in. I had a restriction of 6 weeks before trying, but have never been able to sleep on the surgical side for longer than an hour or two, and it's been 23 months since THR and 8 months since gluteal tendon repair on that that same leg. Check with your surgeon to see if he has any restrictions for you. And when you are allowed to try, you'll know if you can or cannot! And keep on trying on both sides, since things take a long time to fully heal. Both of your legs had replacements, and one side may be easier to sleep on than the other.