I've not followed this season as closely as I would have liked, but it has been disappointing for sure. In reading the posts after the Twins traded a quarter of their roster, mostly for prospects, it seemed that the back channel conversation was about when the Twins would be good enough to contend.
I think they can as soon as next year. First of all, the lineup has a lot of young veterans who could (and should) make a step forward next year. Sano and Buxton have had high expectations, but only about a season and a half of good results between the two of them--Sano's rookie year and first half of 2017 and Buxton's second half of '17--Kepler hasn't become even a good player despite excellent tools and a great swing, Rosario has broken out, Polanco missed half a season with a suspension. I think three or four of those five could be All-Stars or near All-Stars next year. I'm thinking that an acquisition or two of pitchers with what is coming back next year will make the mound corps pretty good. Berrios has a ways to go, but he's had a handful of dominant starts, Gibson has been very good, and even when he doesn't have his best stuff, he's given the team a chance to win. Add a solid starter and then pick from Meija, Pineda, Gonsalves, Odorizzi, maybe Stewart and Slegers to fill out the rotation. In the bullpen, a veteran arm or two with Rogers, Moya, Hildy, a perhaps revitalized Reed are the start of a good pen. There is money to spend so that shouldn't be a problem. Catching should be better with Castro and an improved Garver manning that duty.
There seem to be three or four "super teams" and Cleveland is also very good, but things can change pretty quickly. I certainly hope that the FO approaches 2019 with the idea of contending. I'm too old to wait for rebuilds lasting several years!