How long can snakes hold their breath?

I'm prompted to ask this, because for some reason, my kingsnake has been soaking in his water dish for over 24 hours. He -is- going to shed, but it's wierd 'cause he's never done this before (humidity is the same).

I checked on him earlier tonight and his head was completely submerged. I'm pretty much confident in his ability to keep from drowning himself , but it makes me feel a little uneasy seeing him (and others occasionally) stay under the water for periods of time.

To keep this more corn-related, I found my normal in his water dish a couple days ago - he couldn't submerge his head (believe me, there -was- water in his dish!)

Snakes are one of those animals that diliberately stop breathing during random parts of the day (i know theres a proper name for it but it was so long ago when i did my Bsc) Many of the marine species can apparently "breathe throught ther skin" or rather absorbs o2 across there skin membrane, and snakes being ecothermic and having a low metobolic rate means a snake can hold its breath for a damn long time - i wouldnt be suprised if a normal snake ie corn/king could sit still under water/in a bowl for at least an hour with out coming up for air. If yuo are really interested to find out about it the infomation is easy to find as al the diving reflex /holding breathe stuff was heavily looked into in the 1960's/70's.
I really wouldnt worry about a adult king