TLDR: About two days.
I was sick recently, but I was back to regular lifting and conditioning at near full-force within 48 hours.
I didn’t realize it at the time, but I’m 99% sure it was COVID: My wife, who had similar symptoms a few days ahead of me, tested positive about a week later, and my father-in-law (who’s 83 and with whom we had spent a lot of time), ended up hospitalized with it later that week.
That’s some pretty strong evidence that I did, in fact, have COVID.
Edit: I will just add that only within the past few days have I felt anything close to “pre-COVID 100%” (whatever that means), particularly with respect to my conditioning work. Sometimes I still feel like my lungs are trying to suck all the air out of the room… But maybe we’ll just say I’m working super-hard now, haha!