We are planning our fourth trip from the UK to the US for next year and would appreciate any advice in trying to decide the best time to go. We've previously had fantastic trips to the Denver area and a longer road trip which included Yellowstone and are looking to see some more of that part of the US.

It will be a two week trip and the very rough itinerary currently looks something like:
- Fly into Denver
- Drive to Jackson, WY with an overnight stop somewhere on way (Rock Springs?)
- Spend a few days in Yellowstone area, including visiting Cody, Beartooth Hway etc.
- Head North to Glacer NP, stopping off on way somewhere (Helena?)
- Spend a couple of days at Glacier
- Then a few days travelling back towards Denver, not sure on where will be visited on way, but will include Mt Rushmore area.
- Back to Denver to fly home - may revisit Rocky Mountain NP if there's time (Trail Ridge road was unfortunately closed when we visited last).

Wanting the various roads to be open (Going to the Sun Road, Trail Ridge Road, Beartooth Hway) seems to limit the timescale somewhat. It would be nice if there was still some snow visible on the peaks, as that always makes things prettier. When are we best visiting? Are school breaks etc likely to make roads particularly busy at certain times? (We visited Yellowstone in early September last time and were presently surprised that it wasn't too busy).

Thanks!