I agree with everyone in saying that Foster's is in it's own time zone, where time passes, but no one ages. But it's still a good question, how much time
has gone by since the show started? Putting the the numbered seasons aside-
In "Berry Scary" it must be summer since we see Bloo and Mac swimming. In "Cookie Dough" Mac says "It's the middle of winter". Then in "My So Called Wife" is clearly summer time again given everyone's swimming in the pool. "Camp Keep a Good Mac Down" also feels "summery" to me, which aired not long after "MSCW", so it must be the same summer. Same with "Foster's goes to Europe", since it's hard enough understanding how Mac's mom is letting him go to Europe with people she doesn't know, I imagine it must be summer in that episode too because he's not needed at school. Then comes "A Lost Clause". But then, "A Lost Clause" was suppose to be Bloo's first Christmas at the house (Wilt says so), so it must have been a "flashback" to the previous year. In "Go Goo Go", apparently a whole year had gone by since she first came to the house and got the hint that she really wasn't wanted there. But maybe that could have been a "flashback" type episode, too. But if that was a flashback episode, Bloo would have been at the house over a year by then. Then we have to take into account all the episodes where Mac is in school, so the school year must be in progress. Later comes "Squeeze the Day" , which is also summer, or at least late spring (I feel a Memorial Day vibe personally). "The Big Cheese" feels like fall to me, probably because Cheese brings up the fair, and my experience is county fairs are usually in the fall. But not long after comes "Say it isnt' Sew" when the fair comes up again. Is it the same fair? Enough time has gone by it doesn't feel like the same season. I'm not so sure about that, I suppose... And finally "Nightmare on Wilson Way", clearly it's Halloween, and it's official that Bloo has been in the house for at least one year with the flash backs from last Halloween.
Soooo.... the way I see it, Blooregard has been at Foster's for between two and two and a half years now.
