pneumatic equation

I'm trying to find a particular equation that I came across years ago, but have since forgotten, and probably never knew the name or if it even had a name.

Basically, if you have two regions with different pressures, and a hole with area A between them, how long does it take before the pressures equalize?

I believe you just need the two pressures and the hole area, not the volumes or temperatures, but I may be mistaken. We might also need certain gas constants for whatever gas.

All I can remember for certain was that this equation involved the natural logarithm. Oh well. If anyone knows it, please let me know.

thanks.