I've driven from western Massachusetts (where I live) to Niagra Falls. I believe it was in the 6-7 hour range (but that was a few years ago and I can't remember for sure). Since you will be on interstate highway (Mass Pike to I-90, to NY Thruway), I'd guess at 8-9 hours. If the 500 miles is correct, divide that by 65 mph and you come out with 7.69. Figuring that you will be doing 65 + mph on most of the trip, with a rest stop break, 8 - 9 hours seems like a fair guess to me.
Figure on about 8 or so hours..
I think it took me about 4 hours to get to Albany, NY and then another 4 hours to get to Niagra.. Maybe an little extra here or there.
I took 495 -> Mass Pike (90) -> and then 90 all the way through NY
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