Happily, most of that time was not spent driving.
I had the good sense to check online traffic reports before leaving, and the little map had Highway 36 black (which I'd never seen before) and listed the speed on the segment leaving Boulder as "2 mph". Right! Not going that way!
Normally what I do when 36 is ugly is to take South Boulder Road east to 287, but traffic was pretty slow heading that way, so when I got to the park-n-ride, I just pulled in to the parking garage and parked for an hour plus to let things clear up. During this time I was able to see that there was basically NO movement on 36. Eventually I got hungry, so I drove back up to the grocery store at Table Mesa & Broadway and had dinner there. Took my time eating, started a mediocre SF book (ungripped, I put it back on the shelf when I was done), called home, and then eventually said, well, let's give it a try.
South Boulder & 287 were totally clear the whole way. I didn't get above about 25 mph, sure, but the worst bit was worrying that if I had to stop halfway up the hill (Anderson Mesa?) into Louisville that I'd have trouble getting started again -- and I didn't have to.
Eastbound Hwy 36, by the way, was still completely gridlocked and now blocked off as I drove past it at 10 pm. Glad I'm not one of the ones stuck there!