On most felonies, including this one, four years, if you were actually arrested.
If you are unable to be found, then the time is stopped and they basically have 4 years from when you are found again.
While it is true that the state has four years to formally charge a person once they are aware of the crime, you will likely be indicted within a very short window if this is a Fulton Couty case. The practice in Fulton County is to indict everything and investigate later as opposed to some other counties that take a long time to investigate before indicting.
You should get an attorney involved immediately to see if there is any way to prevent the formal charges from moving forward. You better move fast, though.