The beach TTD sessions that I offer include approximately 100 images. Typically, to accomplish that, I will shoot for about 1.5 hours (just as you thought).
I believe most photographers in this area book out the session as a "TTD session", rather than by the hour. So if they have a TTD package it's not normally a specific amount of time.
I would recommend a few locations for your images actually. In my opinion, it's nice to get some variety in the photos. Most photographers will have some kind of route that they are familiar with and end up at the beach.
Here are examples of the two locations that I offer, just to give you an idea. I would probably just do the session "backwards" so we can start at the beach for sunrise, and then make our way into the area with jungle and ruins, etc. Both examples also include the beach :-).
I hope that answers your question and helps you decide what you'd like to do.
Have a great day!