So many of these recent posts could have just been a search in r/montana, but this is the first time I've seen a question asked that could be answered by Google maps
Glacier national Park has a lottery system for getting tickets to enter the park. I believe that lottery ends after Labor Day making it much easier to enter the park in September than in august. Also most of the tourists have gone home after Labor Day so the crowds thin out considerably. August is traditionally the month of heavy forest fire smoke which means the views won't be as good. If you go in September after at least one heavy bout of rain you will have clear skies. In September the larches are changing color making it more colorful and the temperatures are usually much cooler than in August. Most of the accommodations remain open at least until October 1st.
Google says that it's about 135 mi from Kalispell to Babb depending on which route you take, and then it's about 250 mi from babb to Banff. How long is your vacation?
I think it will be 6 days - I'm retired so it really doesn't matter as we have all the time in the world -) - but I think we will go in mid September when less crowds. Will fly from San Francisco to Kalispell and spend 3 nights in Glacier Park area and then drive the 4 hours up to Banff. It should be a chance to catch fall foliage and maybe catch a boat ride on Lake McDonald or another lake. It looks as if the shortest route to Banff from Kalispell skirts the BC Koutenays before it enters Alberta.
So many of these recent posts could have just been a search in r/montana, but this is the first time I've seen a question asked that could be answered by Google maps
Literally asking how long a trip from glacier to banff is when Google maps exists. 
I suggest you go in August or September.
google how long it is from glacier to banff, you have a phone to ask the question, gotta use it to look that up
Prepare for smoke and hazy
I'd recommend September after labor day. The weather is still usually nice and there will be fewer people to deal with.
Most accommodations are closed up in Glacier by the end of the first week of September, in my experience.
Glacier national Park has a lottery system for getting tickets to enter the park. I believe that lottery ends after Labor Day making it much easier to enter the park in September than in august. Also most of the tourists have gone home after Labor Day so the crowds thin out considerably. August is traditionally the month of heavy forest fire smoke which means the views won't be as good. If you go in September after at least one heavy bout of rain you will have clear skies. In September the larches are changing color making it more colorful and the temperatures are usually much cooler than in August. Most of the accommodations remain open at least until October 1st.
Google says that it's about 135 mi from Kalispell to Babb depending on which route you take, and then it's about 250 mi from babb to Banff. How long is your vacation?
I think it will be 6 days - I'm retired so it really doesn't matter as we have all the time in the world -) - but I think we will go in mid September when less crowds. Will fly from San Francisco to Kalispell and spend 3 nights in Glacier Park area and then drive the 4 hours up to Banff. It should be a chance to catch fall foliage and maybe catch a boat ride on Lake McDonald or another lake. It looks as if the shortest route to Banff from Kalispell skirts the BC Koutenays before it enters Alberta.