The only thing i can tell you is that anybody who gives you a precise answer to your question is probably guessing...
There's no way of telling how long it'll take before we see <10sat/vbyte fees again... In 2018 the optimal fee was >10sat/vbyte for multiple months... This time it could be for a couple of days, a couple of weeks, a couple of months... Or even longer.
I'm willing to bet that it's going to be somewhere 1-2 days after :
Next Retarget (earliest): Monday at 10:10 PM (in 3d 6h 53m 4s)
Next Retarget (latest): Tuesday at 12:33 AM (in 3d 9h 15m 33s)
24h stats Blocks:118That's 26 fewer blocks in the last 24 hours, enough to clean 1/3 of the mempool at this point, one full day and we would be at around 30sat+.
I'm not very sure how legit the following information is, but as far as I know, the mempool would be way less congested and tx fees would be so much cheaper if all of us turned to SegWit. I have checked the stats about how many % of the transactions are done without it and it was significant. A lot of people don't even have any idea of its existence. If I'm wrong, of course, someone please correct me.

Yeah, segwit only has somewhere between 40-45% percent but that alone would not be enough for cases like this or for the future, imagine doubling usage, even with segwit it won't be possible, the solution is to move to a second layer, but that at this point seems ten times harder for new users than simply using bitcoin, and for most people out there even this is quite a hurdle.