I have never been summoned for Grand Jury. Perhaps someone will chime in with how that selection process works.
The fact that Renya asked for a 60 day extension tells me that he knows he has a lot of work to do, starting from scratch. And looking at that 6/30 list as an indication of regular criminal activity, he will have a bunch of actual criminal cases to deal with that happened after 5/17.
Basically the process I saw was the same as a regular jury except that they asked if you could commit for an extended time. About half the pool said no and they were excused. Twice I made it to the selection process and was dismissed once I told them about my education. Once the judge stopped the DA and asked if I was a fair minded person. I said yes and the DA dismissed me anyway. This was in Kalifornia.