I'm going to St. John the last week in July too and have the very same question!

My problem is that my returning flight is at 5pm from STT. Most St. John car rental agencies require the car to be returned by 10am else you have to pay for another day (around $70). So if we return the car at 10am, what do we do until our flight leaves?

And even if we rent the car on STT, perhaps the car return time is the same, making it an even more difficult predicament because now we'll need to get back to STT by 10am.

Maybe it's best to rent the car on St. John and pay for an extra day?

We just did a week on St. John, chose to rent there. Some companies on STT will say not to take the car there, or if they do allow it and anything happens (say a flat tire), it's your problem. It is also more difficult to find 4 wheel drive on STT, which you may want. In our case it was recommended for the driveway to our villa, but there are plenty of switchbacks that also make it desirable at times.

As for departure time, they will inform you that you should be at the airport 3 hours prior to departure. While that is a bit long, it does take a while to get through customs and security. We had a flight at 3 - caught the 11:15 ferry from STJ to downtown, arrived at the airport about 12:15-12:20, took until about 1:30 to get through the lines and into the waiting area. Then we wanted to grab a bite to eat, another long line, eat your burger, and without trying to kill time it's almost 2. Now we read for awhile until they begin boarding (2:40?), and it's not like we had tons of time to kill. Saw more than one person running in trying to catch a plane because they did not leave enough time. Having said that, I think there were more flights leaving earlier, in that 2-3ish time frame, than later, so it might be quicker.

We returned the car around 10, I camped out on a bench in Cruz Bay near the ferry docks with the bags, my wife went off and did some shopping, caught the 11:15. Worked for us. On another trip when we stayed at the Marriot Frenchman's Reef, we had to check out earlier than desired for flight time. We just headed to Coco Joe's (beach bar on-site at Morningstar) with our bags and had lunch and killed some time there. Grabbed a cab when the time was right. If I had more time like your 5 flight I would have considered doing that even though we stayed on STJ.

irbgolfin