We had the same situation last year but had opted for a rent car from Whittier to Anchorage which did give us a ittle flexibility. Made a few stops along the way -a game preserve- another glacier and stopped for lunch at a lovely hotel that Radisson appeared to use for pre and post cruises. Had a nice lunch there and went up on the ski lift, but still had lots of time to kill in Anchorage. Just walked the streets, saw the historical movie, soaked up some fun in the park and then off to the airport for a long wait. A day room would definietly be worth it as it was truly a long day. The cruise was wonderful -you have a lot to look forward to.
Have Fun -Jan