A few Septembers ago, I drove from east to west over Marshall Pass in a rental car. After I did it, someone told me you're not supposed to drive a rental car anywhere but on asphalt. Oops.
It was a great drive and I enjoyed it a lot. I then drove on to Chama and eventually to Albuquerque. The car made it through just fine.
I can't remember how long the trip over Marshall Pass took, but I don't think it was all that long.
If you can, plan it so you have the sun at your back, or at least not directly in your eyes.
IMHO as a flatlander, the last week of September is the best time to visit.