I cannot imagine why you would ever need to arrive 1.5 hours before boarding. If you are going to check bags, you will need to be there probably 45 minutes prior to boarding. If you are not checking bags, 20-30 minutes are sufficient.
Note that the OP is traveling thus: "My wife, 10 month old daughter, and I." He also isn't traveling from the Twin Cities, but rather from some other location where Red Wing also makes sense as a departure point. So he (or she) has to drive some distance.
Add to this construction on I-94 (the Interstate was closed this weekend for various construction projects) and on University Avenue, near the station (light rail going in), and the general friction of travel, especially with an infant, shooting for an arrival 1.5 hours seems pretty reasonable.