The longer the better, i did this with a normal ipod about 6months ago, but it fell into the bath whilst washing me doggy. It was on and totally submerged and bounced off the bottom!
I took it out, strangely it was still on, turned him off and put him in a cool dry place for about 2weeks. Checked him over and he worked fine
My major concern is the screen, that may be written off!