We flew Alaska Air from SFO via SeaTac to Anchorage. You can walk most of downtown in a couple of hours.
Museums take longer.
We could see Mt. Bus to Seward takes about 1.5-2 hours. To see the glacier, we transferred from the bus to the M.V. Ptarmigan for a 20 minute ride up the lake. Service was excellent. Everyone made a point to get our names and use them.