I think the OP will be fine. Especially since you
aren't elite/first class, there's less of a rush to be there right when boarding starts...unless you can snag an exit row when you check-in at 23h:59min. (hint)

The 3-5 minute walk is accurate. Also, the early morning MSP-DTW flights, barring weather or mechanical delays, usually arrive a few minutes ahead of schedule, at least when I've taken them. So you may actually be on the ground closer to 8:30. In summation, I think you will have plenty of time. Enough to go grab a cup of coffee or a snack if you desire.
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