Go to our Winter Park Music Festivals page for a full run-down (or line-up) of artists performing over the weekend, but Walter Trout and the Radicals headline on Saturday, and Trampled Under Foot close out on Sunday. Cool.
I've been to Music Festivals before where too many people start to "exit the building" just as the headline act comes on stage, purely to try and get a head-start on the traffic which, admittedly, can be heavy over the weekends during summer. No real difference to winter, but for me it defeats the object of attending the music festival in the first place. My recommendation would be to attend the whole event and take advantage of StayWinterPark's free night special (if you stay 2 nights) by either checking out late, or indeed going home - if you've come up from the front range - early Monday morning. That way you can stay, shower, and generally chill in your condo and perhaps enjoy a relaxing meal out, and then hit the road at 9PM when no-one is around.
Looking ahead, the Weather Channel for Winter Park predicts highs of 67 on Saturday and 65 on Sunday, with sun and some clouds, more so on the Sunday. Seeing as the current temperature is supposed to be 69, and it's actually 78 out there as I type, it will probably be warmer than predicted. Don't forget that Factor 30 suncream unless you want to crisp.