I called the 800 number and the lady I spoke with told me the P seats are indeed released 24 hours prior, so I will try that first. If that fails, I can either
Try to get on stand by for a flight that leaves for DTW 12 minutes earlier than the one I am on, or talk to the FA once airborne. Either way, I am making that connection

By the way, the rep I talked to at the 800 res center was VERY helpful. Can't remember the name, but kudos to her and the res center!