I think you may be referring to Sun Rider (vs. Sun River). I did a google search for snorkeling in Cabo and came up with several websites. The Sun Rider snorkel time is 10:00 AM - 1:30 PM so that should work well with the cruise ship time line. The boat leaves from the Marina just in front of the Costa Cabo Real Resort (formerly the Plaza Las Glorias hotel). It is about a 10 minute walk from where the tenders drop off the cruisers. We have taken this Sun Rider snorkel trip several times and enjoyed it very much.
Here is a phone number for the Sunrider in Cabo: 011-52-(114)3-2252
There is also a tour company listed that could probably pre-arrange for you and their
e-mail address is: email@example.com.