Officially you can only be excused for emergencies/unusual circumstances - New York Grand Juror's handbook (page 10). In practice, you should be fine, just bring it up as early as possible.

You will be excused but you might not get paid for that day. I would just get it out of the way

I had a conflict while I was serving grand jury duty in Brooklyn and when I asked about getting excused for a day they said “there is no scheduled time off in grand jury duty but it sure would be a shame if you had to call in sick that day”. They were surprisingly flexible for us because they said so many people just ignore summonses and don’t show up at all that they appreciate the people who do because they know it’s a huge inconvenience.

I think you'll be OK. I was on a grand jury in 2017 and there were definitely days in which we didn't have a full squad.

When I got called for the same thing I was leaving the country before the first day of the... trial I guess?

I had to go all the way to the court house to clear this up, and the woman there had the audacity to tell me that I should cancel my flight. When I laughed, she remained entirely stone faced.

I ignored her and got a letter in the mail with another date and a threat, that I didn't see because I wasn't in the country. Nothing came of it though.

I did eventually get called to jury duty again but that time I only had to call in. I called in, some woman read through a huge list of numbers, got to mine and said "call again tomorrow". They did that for two more days, then I got another call where a woman interviewed me about whether or not I supported closing Riker's, which was fucking weird. Apparently Riker's sucks but I'd never heard anything about it so answered pretty much every question with "I don't know", because I didn't".

And then I got a call that said I was released from jury duty.

I did three weeks grand jury a few years ago. My advice- do not tell anyone. On the day of call and let them know you can't make it. Then the next day tell everyone you had stomach problems and couldn't leave the bathroom. If other jury members think you are going to a wedding they will also try to take a day off. After a few days you will know all the court officers and judges and lawyers in charge of you. Don't give anyone your social media. Good luck.

I've been on a grand jury. Lots of people just don't show on random days. You'll be fine. Just don't go that day.

I don’t live in NYC, but I was dismissed from a grand jury in my city/ state. My daughter was 15 at the time and this guy was trafficking teenagers. I wasn’t even there a day. I guess they thought I would be too biased. They were probably right.

You'll be fine. Just let them know if you're selected and they'll let you go. I was surprised with how flexible they were once you're selected. Honestly, it was such a good experience!

Just don't show up or call in "sick".

Long story, but on a grand jury you only need to serve like a certain amount of the days or something like that, and its not the full amount you're scheduled for. Its totally normal for people to miss days all the time or just stop showing up at some point. Nothing to worry about. Take the day off. No issues. Officially you're supposed to be there, but its actually in conflict with what counts as serving, so yes, you can miss days.

That said.. 20 days is unusual. You won't know your actual schedule until you have which specific grand jury you're selected for, on the day you show up and are selected. Most are 10-14 days.