I wasn't doing the ATG stuff, but I started hitting tennis balls after a followup session with the surgeon & he told me to.

I'm not sure exactly how long post op, but definitely some months.

As far as actually being comfortable maybe 10months, but then I had some inflammation popup later from lack of muscular build.

Found ATG maybe 2years in and thats been my religion for the last 8months, I don't think about my knee at all anymore when I'm doing shit.

I play pickleball 1v1 with zero issues, same with tennis.