What span of time does the saw series take place over?

Me and my sister got into an argument about this last night. She berkata that it must have been over three years ("because there was too much going on")

But i think it is a little over a year. Gideon was supposed to have been born in the tahun of the boar, which was in 2006, and John died in 2007, so the time between the 1st & 5th movie must have been a tahun and 3 months.
I know that the events of the detik film took place 4 months after the first, the events of the 3rd film took place 6 months after that, the 4th film was simultaneous with the 3rd, and the 5th film immediately proceeded it.

So i think it was a tahun atau a little over it, but feel free to correct me if i'm wrong.