which cruiseline you are going with?

Both Princess and Royal Caribbean let you book excursions online and there are departure time for each excursion listed online.

Personally we do not use cruiseline land excursions 99% of the time (except may be SCUBA diving when the transportation to diving site is tricky). Cruiseline excursions are usually 100% more expensive than excursions you book with local providers and many times you get much more personalized tours than going thru the "mass". Unless you want to do SCUBA diving in Alaska or Ziplining in Alaska, virtually all other activities you can arrange them yourselves than going thru cruiselines. The providers of SCUBA diving and ziplining have signed exclusive contracts with cruiselines, thus they cannot take in customers not going thru cruiselines.

I would suggest you go to cruisecritic.com site and visit the Alaska forum under Destinations to ask your questions there.