There are no established tipping guidelines for all cruises, you should decide the amount to tip your guide and crew based on your level of satisfaction with the services provided on board and while on excursions.
On Luxury and First class cruises it is recommended to tip $15-$20 p.p. for the guide per day and the same amount per day for the whole crew. On Midrange and Economy class cruises it is recommended to tip $10-$13 p.p. for the guide per day and the same amount per day for the whole crew.
Galapagos is a top-destination for travelers, therefore cruises and tours are on very high demand year-around. It is recommended to arrange your trip at least with 6 months in advance to secure and guarantee your spots on the preferred trip.
Now, if you find the opportunity to visit the Galapagos before 6 months in advance, there is also the possibility to find cruise deals that may fill your expectations. However, if you leave your decision for the last-minute, you may not find what you were looking for a tour that will fulfill your expectations.