MSP snow is supposed to start after noon on 12/8. A 12/8 5:20 am departure should be trouble-free. While UA published a 12/8 weather waiver some hours ago, NW and DL haven't done so as of this posting - in my experience, NW usually waits until it actually starts snowing before considering a waiver for MSP. You never know - sometimes the storms track differently than the forecasters expect....

Now, for your return at 11:20 pm, that could be more interesting.... The forecast says the winds will be out of the NNW - which means landings on the two parallel runways at MSP should be no problem....

As a guess - I'd predict your flights will be on-time.