Well, 3 months is a rough estimate, it's never been said exactly how long they've been in the Grand Line (has it?). Besides, Bon Clay got hot in significantly less time. There is hope! XD

Oh, you knew the Jii-chan thing was going to come up eventually!! Oda answers all...eventually. And again I don't think anyone was predicting this one (even though someone just pointed out that in the original pilot, Luffy's grandpa had the same char design as Garp, and bwaha Oda-sensei you are such a genius, to put it right under our noses all along...!)