Around 7PM-4AM (when streetlights turn on), FPS drops drastically. This affects the title screen too if you stay on it too long.
If using {{revision|3.0-Hashless}} on Mac OS X 10.7 or later then change the EFB Copies to RAM to resolve the game slow down that occurs at in-game nighttime (7pm). It will make the sound choppy, but this can be fixed by switching the sound to DSP LLE recompiler.