Have been wondering this myself for my dynasty league, however; I'll agree with kab on this one, I don't think he is close. FWIW, he's not even on the Twin's 40-man roster. Twins' rotation is far from impressive but they are adequate enough for Gardenhire that he won't look to send one guy to the bullpen or minors yet. As kab said, they have the current 5 (liriano, pavano, duensing, blackburn, baker) plus slowey, perkins, and swarzek that can all be starters.
My guess is that we won't see Gibson until around the trade deadline if/when liriano is dealt. Don't have the quote off the top of my head, but in ST Gardenhire said that Gibson will be in the majors this year, but he didn't specify when obviously. His improved k-rate this year is intriguing, but doubt he will sustain that in the bigs, and he has a pretty high ERA for a top SP prospect in AAA. Would probably compare him to a Jordan Lyles level prospect. The potential is there for big upside, but probably will not be much more than a #3 in real life.