Some schools have their revisit days scheduled in advance and posted in their Admissions calendar. Other schools schedule them once decisions go out. You can usually search and find when last years revisit days were - there was a post here or on each school’s website - and that can provide you with some guidelines. Some schools have 2 days and others one. Some will split it up by year. Some will have a full day program and others a half day.
Last week of March after kids are back from spring break and first week of April before 4/10 deadline to respond is the time frame.