Full diving day from Isabela:

Yes, often done so for dives near this island. 

Boat riding time from Puerto Villamil:

More or less 1.5 hrs. per way.

General itinerary for the day

Diving in Isabela has only started in the last 5 years. There are more companies offering these services, and some that you can really trust regarding equipment and security. The day diving excursion options from this island are: Four brothers and Tortuga Island. Both places have incredible marine fauna and can be done by divers with more than 40 inmersions, with an open water diving license. 

What can you do today?

Boat ride, diving, marine life observation.

Possible / Suggested Overnight Town:

Puerto Villamil.