(1) I assume that if you play it 100 times and spend 10 hours may be and just may be you may complete it once but i just don't see a point in doing it because this mission doesn't count for the 100% ckecklist and doesn't even count for the trophy that you get after completing 5 different plane and ground missions. In my scenario this 2:16 mission came 6 or 7 after i had already completed the minimum requirements for the trophy.
(2) I was just wondering...is it possible to make a QUICK SAFE once the train is in a good position and then just load again and again untill you hit it from the first time and then fly towards the boat?
The train can occupy only 4 or 5 significantly different positions, so, assuming that you have to repeat the favourable position occurance, let's say, 5 or 6 times in order to get the second target, you will probably waste something like 1 to 2 hours on this mission when you're not luky and/or a very good flying bomber, if you want to complete it.
To me, it took more than 1 hour for sure, but I had to do it because I basically could only play with Trevor at the time, and I needed some money on his account in order to be able to do useful things with my playing time (I own half of the game, and the friend I split the cost with could come to my place and advance the main story only once every two or three weeks...).
I'm not sure, but I think I remember that the train's position is randomly generated every time you load the mission, i.e. even when you load from a save-file.
So I think that this method you're speaking about would not work. But, as I said, I'm not sure, since I played those missions long ago (and once you complete that one, it'll never happen again: you'll get only easier missions, and infact the land missions will be more time consuming, if you plan to use the property in order to make some money for Trevor).
So please try it and don't trust my memories on that!