In addition to booking excursions through the cruise line, I work with 4 different 3rd party operators. You may explore options from these for your trip.
All 4 of these companies have a "return to ship" guarantee, and my agency uses them both extensively. My general guideline is to look at the departure and end times. For departure, keep in mind what time the ship docks and what time the gangway is open (that info should already be in your app under calendar). Taking into account where the meet is, make sure you have time to meet them on time. All aboard is usually 30 min before departure, but that time is also in your app now (calendar). Personally, I book trips that comfortably get me back to the ship with lots of time to spare. For example, if all board is 4:30, i plan an excursion that says I'll be back at ship at 3:00.
Keep in mind, if your port is a tender port, you must factor that in. For me, I only book cruise line excursions for tender ports and any port where you must clear customs.
Let me know if you have any questions or concerns.