Most don't. Its not a good idea. I do it but don't advise it. Last winter I hatched ever weekend in one incubator. I had the humidity between 15% an 30% Monday threw Thursday an around 70% Friday Saturday an Sunday.
Hatched between 50% an 75% of what I put in most weeks. I did have a few 100% hatches but I had a few flops as well.
I am doing a staggering hatch with 6 eggs and so far all is good. I kept the humidity around 55% until the first egg was to hatch out. As soon as it pipped, I zapped a wet sponge in the microwave to get it hot. I tossed it into the bator and it raised the humidity level up to 85% in about 45 seconds. I left it there until the pipped egg hatched (8 hours) then I took it out. Humidity slowly came back down to 55%. Next day, next pip, same thing. You have to pretty much stay on top of the bator to do it this way. Its a lot of work also.
I did a staggered hatch for three sets of eggs. The first set was chickens and the second and third sets were ducks. 9 out of 10 chickens hatched, 4 out of 5 ducks hatched, and I'm still waiting for the last set to pop. I ran my humidity at 50% for the whole hatch of the chickens except for the last 3 days. At lockdown, I raised the humidity to 55- 60%. I've kept my humidity at 60% for the rest of the time and now I'm waiting on the last set. They're on lockdown at 60%. I haven't had any problems. All the babies that quit seem to have quit a at day 18 or so.
I know it's not preferable to do a staggered hatch, but I only have one incubator now and it's just how things turned out. Tomorrow is lock down for the first batch and the second batch is a week behind. I've been keeping it at 55-60% humidity, and I was thinking to take it up to 70% for lockdown and keep it there until both hatches are done? Or should I raise it to 80% for the upcoming hatch and let the humidity drop back to 60% until lockdown on the second batch (at which point I'd bring it back up)?
I'd say take it to seventy and once the hatch finishes, drop it back down until lockdown. Then, at lock down, raise it again. I don't know where you're at, but for me, I am able to lift the top momentarily without disturbing the humidity. Also, I don't know if you have an egg turner, but since you still need to turn the eggs, I'd remove the turner completely since you don't want to risk crushing babies. Then, when you're turning the eggs, take a warm damp washcloth and through it over the eggs that you're not turning. It'll help keep them humid long enough to turn your other eggs. This is what I did and it seemed to have worked well. I have pips in my last batch, so I must be doing something right to only have 2 of 15 eggs quit during lockdown.
I do staggered hatches, but I have a 2nd incubator. What happened to me the other day was that I miscalculated my hatch date. I accidentally left the eggs in the turner, and when I looked in to see some of my babies hatching. Anyways, the point of this is that I didn't add any water to my incubator (running at 40% because I am in Louisiana.) I had the best hatch rate ever with the low humidity. I also have noticed that the humidity raises on its own when the first baby hatches. I would try and meet in the middle with humidity. Also, I would put the non-hatching eggs in an egg carton while the others hatch so that they don't get kicked around.