What works for me, here at the top of N. GA at 2000 ft elevation in the mtns is to keep it from 40-50% the first 18 days, then 65-70% from Day 18-hatch. If it goes up to 52%, I dont sweat it because it will naturally begin to go down soon. IF it goes to 30%, I dont panic, just add some water.
A range is fine, not specific numbers. If you try to make a game of keeping it as close as possible to 50% the first 18 days, then raise it over 60% but below 70% the last three, you'll probably be fine. The effort it takes to do that in a low humidity environment will be more, though. Im on Day 4 here and the outside humidity has been very low for Ga, about 15-20%, and created a challenge.