Invited to a wedding but also just started a job, advice ?

Same with my wedding day! It’s coming up in 87 days! Then a month in a half later we’re going on our honeymoon for a week!

Best alternative would have been to say when accepting the new job, "I can start on X date, if I can just take off for a wedding on Y date." But it sounds like that opportunity has passed. At this point, all you can do is throw yourself on their mercy and say something like, "I know this is awfully soon after my start date, but could I possibly take off that day, even as unpaid leave?" I'd suggest asking before you start working, rather than waiting until the first day.

I agree with PP that I would have said something when hired. Contact them ASAP and yell them you forgot to mention it and tell them it’s a family wedding.

I would have mentioned it when you accepted the job, that you have a prior commitment on that day. They would have understood. I would ask them ASAP, and just say hey, I totally almost forgot but I have a prior commitment on X date, would it be possible to have that day off? The worst they can say is no, in which case the sooner you can let the bride know the better, so she won’t have to pay for someone who won’t be able to attend.

I would just talk to your boss immediately and see if it's an option to miss work.