Ive been to USS both on weekends n weekdays i would say weekdays are crowded as well but not overly crowded so no worries but best to go on weekdays

And you only need 1 day for USS if you plan accordingly, depends on everyone, im in my 20s so i do not sit rides like treasure hunt or the small roller coaster on the dragon near shrek's castle!

When you guys head to USS Do find out the time for
"Monster Rock"
"Water world play"
"parade" I think this is around 6.30PM

The top 2 only plays during certain time and please do not miss it or it would be a waste for water world do sit infront and enjoy getting wet!