I think Lazarus is right on for most cartridges. However, I have owned a few that still sounded pretty bad even at 30 hours of break in. The other thing to keep in mind is cartridge loading as well as VTA. Both can play a major roll in soundstage and openness. The nominal cartridge loading is just that--"nominal" and almost never optimal. You have to experiment a while to get the best sound. However, get at least 10 or more hours on the cartridge, because any changes you make during the biggest changes during break in will likely be changed again.
