Discover Magazine linked to a new study that suggests that no matter what their size, it takes most mammals about 21 seconds to urinate.

Using high-speed fluid dynamics videos and flow-rate measurement at Zoo Atlanta, we discover the “Law of Urination”, which states animals empty their bladders over nearly constant duration of average 21 seconds (standard deviation 13 seconds), despite a difference in bladder volume from 100 mL to 100 L. This feat is made possible by the increasing urethra length of large animals which amplifies gravitational force and flow rate.

If you're into that kind of thing, here's video proof. (NSFW, if slow-motion animal peeing is not allowed at your workplace for some weird reason.)