In the original story, Luffy set sail on his birthday, May 5, 1500 in the Sea Circle Calendar. He met Koby later, but only after drifting at sea inside a barrel for over two weeks.
After that, the Straw Hat Pirates traveled from the East Blue to the Grand Line, picking up crew members and dealing with trouble along the way. Even in a straight line, the journey would have taken at least a month. From entering the Grand Line through Reverse Mountain to reaching the Drum Kingdom and receiving Ace's message would have taken another ten days to two weeks at minimum.
Two months before they received that message, around the time Luffy first set sail, Blackbeard attacked the Drum Kingdom and Wapol abandoned his people to save himself. Ace came to the Drum Kingdom in pursuit of Blackbeard, then asked someone to tell Luffy, who had already entered the Grand Line, that he would wait for him in Alabasta for ten days.
After that, they knocked Crocodile flying in Alabasta, met "Hyena" Bellamy in Mock Town, and beat the "God of Salted Fish" Enel on Sky Island. Only then did the story reach the point where Blackbeard defeated Ace and handed him over to the World Government in exchange for the title of Shichibukai.
Loa had flown several circuits around the Grand Line and measured the distance himself. Aboard the Going Merry, it would have taken the Straw Hat Pirates more than two months to cover it.
And that was under ideal conditions, without counting any detours along the way.
In other words, Ace should not have been captured until the end of this year—October at the earliest! Then Kuma the "Tyrant" would scatter the Straw Hat Pirates at Sabaody, and they would not set sail again until