Agh, sympathies for the nightmare.
1. Testing for "okay to hang out for now":
On the virus.sucks web site they say
"While there is no "golden rule", many users have successfully avoided household infections with a re-test window of ~12 to – at most – 24 hours." So I usually would re-mask after about 12 if not re-testing.
2. Testing out of quarantine:
It's hard to get reliable data on this, but from what I've seen, it seemed like most people would have detectable virus 3 days after they caught it. (If anyone knows better, I'll be very interested.)
So, not saying this is absolutely guaranteed safe, but after possible exposure, we have been doing "4 nights bubbling separately, then Pluslife test the next morning".
The extra night is because, by the time we've done 3 days of carefulness, for me I feel like it's not that much of a hardship to wait one more night. But that feeling is partly because I can have a room to myself to sleep, so "separate bubble at night" doesn't involve any masking, except if I nip to the loo in the middle of the night. If I had to, or specially wanted to, share a room at night, then I might risk simply counting off 3x24 hours, rather than sleeping masked which I find difficult.
Disclaimer, this regime has not been tried against actual infection. When I got covid, it was before we _had_ the Pluslife.
3. Also from the virus.sucks FAQ:
"Covid tends to show up in throat samples much earlier than in nasal swabs, which is why many Pluslife users perform a throat swab or combined nasal and throat swab to detect infection as early as possible."
Wishing you luck!