If NJ grand jury is anything like NY grand jury it is very different from regular jury duty. I have done both. Grand jury is you hear from the prosecutors and witnesses about many cases and decide if they justify an actual court jury. I had it for 9 weeks also but had to report 3 days a week. You do still have to go through a screening process but it is not specific to a certain case until before you hear that case. I heard about 50 cases and was excused from 1 since I new the victim. Just like jury selection I had to call on the days I was to report and see if i was needed but found that if I called most of the time I had to report, and I did have to do all 9 weeks. The deal is if anyone has been charged with a crime you help decide if there is just reason for a court date to be set.
Day care was hard to figure out. I set up 2 people for each day and told them I didn't know what or when the time schedule was or if they would even be needed. I used family members who were also stay at home moms and grandmas. Since you already work, just line up who can pick up the children or be at you house when the bus drops them off.
The only time I had to report in the afternoon was for grand jury selection. Once I was selected I had to report from 9 am to 4 pm. Sorry for the bad news but I did find that when it was over with I felt like I had served my country.