We've never been to Universal and have one day planned the day after Presidents Day. I read somewhere that Tues is the least crowded at Universal. We are going to get the park hopper (or whatever it's called there) and our only priority is both Harry Potter parks and the train between the two. This is doable, right? Anything else is an added bonus. It's me and my 15 year old daughter.
from when i went, it is definitely doable if you only hit the harry potter parts! While youre in the WWoHP, it looks like you waits will average 20-40 minutes! the overall crowd levels are going to be moderate, not light and not heavy, so i couldn't imagine any walk on rides except for like ET or Ollivanders if you count that as a ride.
you can probably do other rides not in the WWoHP but you should probably pick them out before you go because its easy to get carried away.
tips from me: try BOTH butterbeers, but the frozen is WAAAY better. also the butterbeer cup is truly worth it! the fudge is really good from Honeydukes, and my friend told me that all of the ice cream flavors in US have weird names, but they all taste really good!
oh and, eating at the Three Broomsticks or Leaky Cauldron is WORTH it! The restaurants are themed inside, and it tastes like a good ole hogwarts feast. Also, drinking a butterbeer at night looking at Hogwarts with the lighting on it is my fondest memory of WWoHP, i recommend staying til dark to see the harry Potter parks at night, i dont know why, but it made it feel way more magical.
Finally, if the butterbeer lines are too long, go into the Hog's Head, they sell butterbeer and there's never a wait.

have fun! harry potter world is the best