I am starting up again after about a 3 month layoff, which I do almost once a year now, and I find in about 4 to 6 weeks I can get myself built up to close to where I was before the layoff.
Of course, I have been training over 30 years, so If muscle memory is real, it works great for me !!!
I always train heavy and always natural. Always.
P.S. I dont seem to experience a lot of the joint problems others do, probably because of my layoffs. Good luck !!!