Upvote:3
One general option - not mentioned in the comments - is to look at historical delay information. How often is the plane late, and how late is it? This is available on a number of websites; I'm a fan of Flightradar24, which shows accurate runway to runway times, but Flightaware is another good option - especially in areas where airlines actually update their systems (in my current locale this behaviour is patchy at best...)
So, taking your flight from GGT-NAS as an example, and assuming you're talking about flight UP373 - which is now scheduled to arrive at 19:40...
Flightradar shows, over the last 5 flights flown, a minimum delay of 5 minutes, and a maximum one of 1h25m. And remember, that's the time the plane landed, not the time it got to the terminal - although in this case, the difference isn't huge.
Flightaware shows similar details - delays from about 4 minutes to 1 hour 28 minutes over the last few flights it has data for.
In both cases, you can pay a few dollars to see more information, and Flightaware will also give you 4 months of history just for registering.
Does this tell you everything? Not quite. Delays might be more common at certain times of the year (hurricane season perhaps). Maybe a schedule change will increase or decrease future punctuality.
But armed with this information, some details about the airport in question (as you say, Nassau isn't exactly JFK or Frankfurt), and an idea of your appetite for risk, you can decide whether to take a chance. In this case, I probably wouldn't (especially as there now seems to be a second airline with nicer flight times back to Nassau).
Finally - how does a 30 minute flight have such a long delay? Simple. It's the end of the day. The plane's been flying around for something like 14 hours, and those 5 or 10 minute delays here and there, problems with getting luggage on and off, delays for takeoff - they all add up.