Since KI is open until 10:00 pm tonight, and since today is a Math-Science Day and the weather is good (i.e. hopefully the park will NOT be closing early!!), could I go up to KI at, say, 9:45 pm and would the season pass processing office still be open assuming KI was also still open as well??

The season pass page says the processing center is open 4-8 PM Monday-Friday and during park operating hours on weekends. I would say these hours still stay in effect even though the park is open but i would try to either get there earlier or try to call the park to verify these hours unless someone else on here knows more