Days are no shorter in Nova Scotia during September than they are anywhere else: 12 hours day, 12 hours night on the euquinox late in the month. Longer days before that; longer nights after. It's the rules of the game, and can't be altered (or at least, not this side of the equator).
I've been up there late in September and seen horrendous heat, e.g., near 90F/32C, with sweat and bugs and all the rest....until it started raining and blowing and in other respects acting like autumn. Hard to predict in advance, but by the time the leaves are really turning you'll see some frost at night. If this offends, show up earlier. If not, it's very pretty in early October.
Hope that helps.