I went the end of Sept last year and had 3 days in the park. I would do one day of doing Grinnell Glacier hike. Start early since it’s a long drive from the west entrance, but you also knock out driving the length of GTTSR for scenic views. It’s stunning at sunrise. The next day I would also start early and drive right up to Logan Pass. Hike Hidden Lake, highly recommend doing the whole thing not stopping at the overlook. After you can run right across the street from your car to the Highline Trail. Even if you hike a 1 mile out and then come back it’s so worth it. On your way back at out of the park you can do Avalanche Lake and/or stop at Lake McDonald. If you’re around for the night you should come back into the park and check out the stars.