I like to open with "I know crunch happens. It's part of our industry. How often would you say crunch happens here and when it does happen, how long does it last?"
At bad companies, they'll justify how crunch is unavoidable but don't worry, their stock is gonna make you Rich(tm). At good companies, they'll crunch a couple times a year, for a week, maybe two. At the best companies, they'll talk about how their Process eliminates crunch time.
I've asked this question ever since I interviewed at a place where the lead dev had a cot in his office.