The Boveda method seems to be the most popular, easiest, and most foolproof.

Keep in mind, Boveda packs can vary if they are over/under charged.
Even some of the best hygrometers are +/- 2 RH %
Should still be close enough for cigar storage purposes.

I used to use the salt method, but many report having issues with it. Results in 75% RH for calibration comparison.
Having a scientific/chemical background, I did not have problems.

In a closed environment, like a zippered bag, which are not fully airtight, it should only take a few hours, but 24 hours should ensure it is stable as long as temperature doesn’t fluctuate. The smaller the container or enclosure, the quicker to equilibrium. Just need to leave it long enough until you don’t see any more changes in the reading.