After-hours dropoff arrangements are supposedly available at that location according to Hertz's website. Just ask them at pickup about what the procedure is.

That said, you'll want to call them during business hours at 617.244.0801 to confirm that you will not be charged extra for returning out of hours. Hertz is one of the companies that can be annoying about this sort of thing. For example, if you're renting from Fri at 5pm until Saturday at 5pm and the location is closed and doesn't reopen until noon on Sunday, you'll end up getting charged for an additional day since they won't check the car in until they reopen.