It’s not the end of the world if you can’t go. My kids went to a total of three admitted student days. Ultimately neither of them ended up at any of the schools.
If you can’t make those days, it’s just as helpful to contact the Admissions office and ask them to help arrange a special day just for your kid. At one college, my D had a sort of guide for much of the day. He took her to a club meeting. The Admissions office arranged for her to sit in on two classes and had another student join her for lunch. She enjoyed the day, but the school she ended up at, she only had one visit in the summer with no kids back yet.
Do what works for you. The college will try to accommodate your schedule in some way I think.