It varies for me. Most of the time, it's probably in the 15-30 minute category, so that's what I chose.
On occasion it can take hours. Or if I've taken a nap sometime during the evening, I can forget about getting a good night's sleep. I try to avoid the nap, but sometimes I'm just so tired I can't stay awake. In those cases I try to sleep through the night, but often I'm not very successful.
