DieselMartini

I have a cruise coming up in January and I'm trying to book an excursion through a 3rd party (it's not offered by the cruise line). I want to make sure that the start and end times of the excursion are within the hours that my ship will be docked in port. The site where I'm booking the excursion lists the local time for the activity, and the cruise line's itinerary shows our arrival/departure times for the port in what I assume is ship time. Is there a way to find out what ship time will be relative to local time prior to my sailing? In case it matters, I'm sailing on Royal Caribbean's Navigator of the Seas, and the port in question is Puerto Vallarta, Mexico Thanks!