User blog comment:Bankai99/That's Some Real Devotion/@comment-3279487-20111107011717

The time doesn't flow as you said, there is no reference but definitely not a single day, remember that there are a few days of Zoro's rest after thriller bark and the events of Strong World in the middle (which is canon) plus the time of sailing (off screen). Yes, it's not long but they aren't strangers as you think. For Franky's and Brook's reasons I'd say:
 * Franky's dream is to build a dream ship (the thousand sunny) and make it so by sailing through the whole grand line, so he have to stick with the crews for doing it. You have to consider that he had taken a linking for the crew since the events of Enies Lobby, plus other reasons that I think are written even in his page here.
 * Brook was alone for 50 years, then he meet Luffy who accepted him, taken his shadow back and give him news of Laboon, so at least he is in debt with him. His dream is to complete the voyage around the Grand Line to meet Laboon again so he has to stick with Luffy too (though he could have went back to Laboon to say hi during the 2 years, but that wouldn't have been romantic would it?). Yes he doesn't know him very well, there was even a filler episode about "Brook' struggles" but he has a very sense of loyalty and gratitude.