When we set up the first things that are unpacked are the instrument stands. The guitars are hung on the stands and left while we set up PA's and drums. We then tune and get a drink. Once we do our mic checks and get the sound set we retune and wait for the gig to start.
Since our instruments all have inline electric tuners we worry a little less about acclimation and the effects on tuning.

Alaska Mike is quite correct about openning a cold guitar in a warm (hot) pub. I've seen spider webs run through the finish of a Humming Bird and it is neat to watch only if it is someone else's guitar.

A little common sense goes a long way in this regard.

Don