At a groundspeed of 155 knots I get over 10 hours of flight time (1600
miles). You are going to typically have headwinds (but you never know,
I had tailwinds coming Maine to Colorado, THE WHOLE WAY), but I was
LUCKY and it was summer. Add in at least an hour for lunch and fuel
and THAT is one looong day. I wouldn't want to fly in IMC or at night
the last 200 miles of that trip. If it's IMC in the mountains of New
Mexico, it usually means ice, especially this time of year. Anyway, I
take it you aren't familiar with the terrain, so I don't think you want
to fly the last leg at night at all. It's great scenery, who wants to
fly after dark over such great scenery! I'd take it easy and do it in
two days and enjoy myself. No tellling ahead of time what the weather
will be, but as your trip approaches, start watching the frontal
systems and time your trip between fronts. It's the Southwest so it's
flyable more days than not, still it's iffy. Such a trip always depends
on the weather.