I don't have a car so I use the LIRR at least a couple of times/week. By taxi, the Greenvale train station is about 5 minutes from campus and the westbury station is about 20 minutes from campus. The Roslyn Taxi company charges $21 for NYCOM to Westbury train station and I think $11 for Greenvale. Roslyn Taxi's phone number is (516) 621-1111. Try to call 1 hour in advance to make a reservation. There is a taxi service in Westbury that I used a few times but the dispatcher is rude and they charge about the same I think. I use the Roslyn Taxi service for either station. When catching your train back add 20 minutes to the driving time since sometimes the taxis are 5-10 minutes late and traffic in LI sux.
My suggestion is the Greenvale station. Check the LIRR schedule since the trains run about every 30-1hour sometimes with a 2 hour break in the schedule.
LIRR fare from NYC to Greenvale is about $6.50 each way if you purchase the ticket before boarding.
If you take the LIRR from NYC you will have to transfer in Jamaica queens going to either station.
Last year we were not really able to predict the exact time/order of interviews so maybe you need to bring that up at the start of your interview. Last year I ran into a nice group at my interview and we shared a cab and took the LIRR back so we waited for each other to finish interviews since there was no rush.