While a longer exposure will produce greater noise due to heat, I wouldn't necessarily agree that in-camera noise reduction is the solution.
I personally never use in-camera NR, as the camera takes a dark exposure which lasts the same amount of time as the original exposure, and then applies dark frame subtraction.
Noise reduction is something that can be done in post-processing by a far more powerful CPU than the one inside a camera, and I don't spend two hours taking a one-hour exposure.