How long do I bake a stuffed butternut squash at 325 degrees with a fresh Turkey when the squash recipe calls for 2 hours at 375 degrees?
The way to approach this is to ask how much hotter 375 degrees is than 325 degrees from the starting temperature of the food, then use that factor to multiply the time. 

Doing the calculations, if your food starts out at room temperature (assuming 65 degrees) then (375 - 65)/(325 - 65) = 1.1923, or 1.2 rounded up a tiny bit. So 120 minutes * 1.2 = 144, in other words 2 hours and 24 minutes. It's a rough calculation, but I've used it pretty successfully.