Waiting over 30 minutes for a slide is exceedingly rare, even when Blizzard Beach has “closed” to capacity, most slides have a high enough capacity that I’ve never found myself waiting for more than 20 minutes or so.
Of course, some lines will be outliers, but as long as you don’t hit a streak of bad luck, waiting 30+ minutes should be rare.
Here’s some notoriously slow lines, IMO:
Blizzard Beach:
Runoff Rapids (used to be a people eater, but that conveyor belt is SLOW!)
Downhill Double Dipper (this is a racing tube slide with only two people going down at a time)
Typhoon Lagoon:
Crush n’ Gusher (capacity isn’t horrible, it’s just extremely popular and the slide is decently long)
Gangplank Falls (again, capacity isn’t horrible but this line is usually decently long)
Now you’re right that spring break, with this benefit in place, will probably be VERY busy. But it’ll be very busy for a waterpark, not on the same level as a theme park really. If you do decide to “rope drop” the waterpark at 10am, you can get a really good seat and knock out most of the slides if you really want. And even if the parks are really busy, there’s a ton of stuff that won’t ever have a line. The wave pools, most of the stuff in Ski Patrol Landing (and the kiddie areas), and lazy rivers just to name a few.
You can read the spoiler if you want some information on what slides should be possible (without a height requirement).
Blizzard Beach:
Mat slides: Toboggan Racers and Snow Stormers.
Runoff Rapids (three slides, two open and one enclosed. Only requirement is that you have to be able to hold onto both handles. It’s a traditional inner tube in size, but has a little bump on the back for a backrest. Open slides are slower.)
Teamboat Springs (Crazy long family raft ride, lots of fun! Only requirement is you have to be able to hold onto at least one handle. This line can get pretty long, so you’ll have to eyeball it. You can always go down to the mat slides if this line is long)
Tike’s Peak/Ski Patrol Landing: Very few height requirements, and the height requirements are generally pretty short. Smaller slides with some cool ropes courses and a zip line.
Typhoon Lagoon:
Keehaul Falls (used to be a kiddie slide, but now it’s open to “all”. Fun inner tube slide through the mountain that picks up a little speed at the end. Regular inner tube size if not a little smaller. Have to be able to hold onto the handles.)
Mayday Falls (also an inner tube slide, but it’s pretty rough with all the “rapids”. Just have to be able to hold onto the handles.)
Gangplank Falls (an older family raft ride, pretty short in height but fun. Small drop at the end, but nothing noteworthy. Just have to be able to hold onto one handle)
Miss Adventure Falls (the newer family raft, also quite fun. Just have to hold onto one handle)
Storm Slides (No height requirement to my knowledge. A set of three pretty standard body slides through the mountain. Each goes through at least one “cave”, but the caves are short.)