Oh yes we do! (and I know you jest) I've written a bunch of them in my not so humble opinion! And @felt.buzz is a master at it.
One trick to knowing if stories got done in five minutes (or thereabouts) is in their lengths - my true five minute freewrites have never contained more than 200 words. And there is a lot of value in being able to write a contained story in 200 words or less. For my next wewrite contest, I might make an even lower word limit, cuz I thought quite a few of the entries could have been told in far fewer words.