Thank you for the responses. I live in the Loma Linda/Redlands area - the very far suburbs of LA. I assumed most people on this sight would not know Redlands and so LA is much easier in terms of reference point. I have made it to Vegas in 3 to 3.5 hours before. Many of you made the point about Friday afternoon traffic, which I was not taking into account.
I make it a point to never leave for Vegas after about noon on a Friday. We usually take off about 8 or 9 in the morning. On the few times that I have left on a late Friday it has taken me 5 to 6 hours, and once much longer when they closed all lanes down to airlift someone after a terrible accident.
So probably will stick with the plan to leave on Saturday morning and get to Salt Lake City in one long day.
I would love to get some recommendations on what to see/where to stay when we leave SLC on the way to Glacier. We would be leaving SLC Sunday morning and need to be in the Glacier area by Monday late afternoon.
Again, thank you so much for all your assistance and your feedback. Much appreciated!!