I'm in the last stages of a staggered hatch just now and while the first eggs set developed and hatched fine, the second lot are looking rather dubious. I think the raised humidity through the first eggs' lockdown period may have had an adverse effect on them. If you have a second incubator to use as a hatcher you could avoid that problem. Other folk on here have mentioned running staggered hatches at a constant 50% humidity throughout. Apart from humidity issues, I don't think it really matters how many days apart you set eggs if you're doing it all in the one bator.
Someone else mentioned to me about setting eggs every seven days. That way if you're using a separate hatcher, you have three days for lockdown, three and a half days for the hatch, and the half a day left just gives you enough time to disinfect and clean out the hatcher before the next lot of eggs go into lockdown the next day. I thought that was an excellent way of doing it. If I get hold of a second bator, that's what I'm going to do.