I have the opposite problem, I'll be going ahead 2 hours (Chicago) lol
I was just going to temp at the same time per say - set the alarm for 8 Chicago time, since it would be 6 Seattle time. I don't know if that would work for you, since it's Vegas and I am sure you won't be getting that much sleep

As long as you can take it after you had the 3 hours of sleep is what is important, and then of course make note of it on your chart that it was not at your usual temping time - your chart won't be perfect, but you should be able to see if there's something up or not.
Have fun!