Welcome back, Maria! San Juan is a beautiful city, especially the area of Old San Juan. There is so much history and culture to encounter there, I'm glad you're considering this tour. I loved my visit to Old San Juan!
When you log into your reservations 75 days prior to setting sail, you'll be able to go to "My Cruise Activities" and then select your San Juan day. There you can select Port Adventures. If you'll notice, there will be departure times listed on each Port Adventure, specific to your sailing. Since I can't view yours, I don't know exactly what departure times are available and offered for that Port Adventure. If you find that the departure time is early enough, you could enjoy a late lunch on your own after your adventure concludes, but before you need to be back on the ship. Or, if your adventure begins in the late morning, you could head off the ship early and enjoy breakfast at that restaurant instead, as the port is near Old San Juan. Another option is to take the shorter two and a half to three hour
Bacardi Rum and Distillery Tour (not the combined one with the Old San Juan tour), so that you have more time to explore Old San Juan on your own before or after the adventure.
I believe that in San Juan, the ship's All Ashore time is usually around 7:45 a.m., and All Aboard is usually around 4:45 p.m. But, please verify that on your itinerary for your exact sailing, as these are always subject to change.
I hope that helps as you continue planning, Maria! Have a wonderful cruise and enjoy your Port Adventure in San Juan!