Transportation logistics for a day trip to Vieques

Hello,

Me & my wife are going to travel to PR for the first time for a week during end of this month (which I suppose is peak vacation time). We are visiting from Boston.

We really wanted to visit Vieques to experience bio bay kayaking & hence have booked a VAL flight into Vieques and a ferry ticket back on the last (9 PM) ferry. Our bio bay tour is from 6.30 PM & the operator says it's going to take 1.5 hours to complete. I have 2 questions regarding transport on the island:

1. I know it's going to be tight returning back to catch the ferry on-time, but this was our only option as we have other activities planned the day after in main PR island. To all the experienced redditors in the group, do you think we will be able to make it to the ferry terminal on time? What are some things we should do to maximize our chances of making it back? I read a few posts suggesting to take the driver's number and call them on time to pick you up and drop you off.

2. We were unable to book a car due to these last minute planning & have gotten a reservation for an ATV, which we plan to use from 10 AM to 5 PM to explore the island (we thought it'd be a unique experience to do so). As we are completely new, what are some things we should take care of?

Your help is greatly appreciated!!