Check the operating hours before you build an evening plan
Magic Kingdom hosts private graduation events on a number of weeknights in May, and on those nights the park closes to regular guests several hours earlier than the published seasonal pattern would suggest. A touring plan that assumes a 10 PM close and finds a 7 PM close loses three of its best hours — the ones with the shortest waits and the coolest temperatures.
Pull the operating calendar for your exact dates and mark the short nights before you assign parks to days. Put Magic Kingdom on the nights it stays open late and take EPCOT or Hollywood Studios on the nights it does not.
The counterintuitive consequence is that a Sunday or Monday arrival often works better than a Thursday or Friday one in early May, which is the reverse of the usual advice.
This is the window to use if you cannot travel in September
The two genuinely excellent value windows in the year are early May and September, and they solve different problems. September is quieter and cheaper but hot, wet, and inside hurricane season. Early May is slightly busier and slightly pricier but has none of the storm risk and better evenings.
For anyone who cannot travel during the school year for weather or work reasons, early May is the answer, and the flexibility is worth spending on. Moving a trip from late May to early May typically changes the ticket tier, the hotel rate season, and the crowd level all at once.
The practical booking heuristic: aim to have departed before the Friday of Memorial Day weekend. Everything before that line behaves like spring; everything after it behaves like summer.
Flower and Garden's quiet weeks are its last ones
The Flower and Garden Festival runs into early July, and May is when the crowd finally leaves it while the installation is still fully in place. The topiaries are past their April peak but the Outdoor Kitchens are all operating and the queues at them have collapsed from what they were a month earlier.
This is the best month of the festival for anyone who came for the food rather than the horticulture. A May weekday afternoon around World Showcase is a genuinely relaxed way to eat, which is not a sentence that applies to the same festival in March or April.
Garden Rocks concerts continue through the festival run. Weeknight shows in May have standby seating available in a way that April's weekend shows do not.
Florida heat management starts here, not in June
The Orlando normal high crosses into the upper 80s in May and the humidity comes with it. The mistake is treating May as a spring month and running the same nine-to-nine schedule that worked in February. It does not work, and the failure mode is a family that has one bad afternoon and then rations the rest of the trip.
Build the day in two blocks from May onward: park at opening through roughly 1 PM, out of the park from 1 to 5, back in for the evening. At Walt Disney World the return leg costs you real transit time unless you are on the monorail or Skyliner, which is a reason to weight hotel choice toward those lines specifically for a warm-weather trip.
Water parks become worth a full day in May rather than a half day, and they are least crowded in the first two weeks before the summer schedule begins.
Disneyland's soft weeks are hiding behind the gray
May gray keeps Anaheim mornings overcast, and a meaningful number of visitors reschedule Southern California trips away from May because of it. That is a gift to anyone who does not care what the sky looks like: the marine layer keeps temperatures in the 60s until early afternoon, which is close to ideal for the outdoor queues that are the resort's real bottleneck.
The quiet stretch runs from the end of California spring break to Memorial Day weekend, and midweek days inside it are the last easy Disneyland days until late September.
If a nighttime show is part of the plan, note that the marine layer can also affect visibility for aerial effects on some evenings. The daytime trade is still worth it, but do not build the entire trip around a single fireworks night in May.