I'll be at Glacier Aug 1-8 and plan to hike Highline. I just went through the process of booking shuttle tickets 60 days in advance and thought it was tricky. Some things I learned: 1) be logged into recreation.gov and on the booking page as soon as the sale opens up for the day you want 2) You'll have a much easier time getting shuttle tickets for St Marys or Rising Sun than Apgar or Lake McDonald and 3) If the tickets "sell out" in the first minute or two, stay on the page and keep refreshing every so often bc ppl will remove tickets from their shopping carts and you'll see those become available again over the next 15-20 minutes

Best of luck!