Hope I'm interpreting your question correctly--are you asking if you can schedule interviews mainly on Fridays? Interviews could be a bit tricky if there's no flexibility in your schedule. I applied last cycle, and some of the interview requests gave me several dates from which to choose, some only gave a couple dates, and some just assigned me a date without asking my availability (which, theoretically, you could call and ask to reschedule, which some people have done with mixed success--some schools basically won't reschedule you or you have to wait a couple months for a new slot). Some schools, like MSU, had designated Friday interviews for out-of-staters who had to travel, which was nice. Offers of Saturday interviews are a rarity (I didn't encounter any in the 20 schools to which I applied).
If you can take a week off occasionally, you might be able to cluster a few interviews together (just be careful that you allow for travel time and consider the level of energy needed to do your best--I personally found that doing 3 interviews back-to-back was exhausting). Good luck!