That’s generally right. In Fulton County they sit for two months. There were two different grand jurys here, though.
There was a Special Grand Jury who met for 8 months and investigated the specific crimes related to the Trump case. They issued a report in January detailing all of the evidence that they heard.
In GA, though, a Special Grand Jury can’t issue an indictment. The report was passed to a normal grand jury who heard all of the evidence, then issued the indictment. That grand jury was first seated on July 11th.