Haha, that is hilarious. I don't think this game will be beatable at 100% in less than a month and that is for someone playing it nonstop, 7 days a week for 12 hours a day.
Think about it this. You know how long it took you to find all the hidden items in San Andreas, right? Now, taking that into consideration, GTA 5 is bigger than the last TWO GTA games COMBINED or 3 1/2 times bigger than Red Dead Redemption!!
Watch this to give you an idea. The game is HUGE.
Looks like it will be around the size of the map on Just Cause II. If you haven't played that the map is stupid how big it is.