robface
How crucial is it to visit Tuck?
Do I need to visit?
If I visit after submitting, does it still "count"?
Tuck is a huge school on fit. They prefer US based candidates to venture out to Hanover for the applicant initiated interview. I would say visiting is huge. If you can only visit after you submit, I think that would be fine. I would just make sure you register for a tour and class visit.
I am assuming you have not interviewed yet. I would just shoot a note to admissions, telling them why you could not visit prior to the deadline, but will be visiting on X date. If you could arrange your interview then that would be great. Not sure how helpful this will be, but from all the research I have done Tuck wants to make sure you know what you are getting into. Hanover is not the easiest place in the world to get to, so they want to see people make the effort to get to know the school.
Hope that helps. Good Luck!