Smallest interval worth sleeping for?

You wake up and check the clock. You don't have to be up for X interval of time.

What's the smallest value of X that's still worth going back to sleep for?

(If different) What's the smallest value of X that will leave you feeling more rested?

So, mushrooming?!

Hey, folks. Or at least those who are getting together to hunt mushrooms on Sunday. Is there any agreement on where to go? The current choices (I'm eliminating JHP because there didn't seem to be any interest, and y'all don't need to deal with my nostalgia) are:

Arboretum, Interlake Park -- city parks, but city parks with a very high probability of honey mushrooms

Something mountainous but close, say, Wallace Falls

Roslyn area -- long drive, highest probability of chantrelles, wonderfully mycologically active site.

Thoughts? There's been at least one vote for "local" and another for "likely to have edibles".