I left DD1 at 10 weeks for a wedding. But it was only a few miles away, she was with MIL (who is fantastic and looks after children for a living) and we came back to her that night.
I was EBF so took a lot of work pumping, especially as had to use some milk to practice the bottle several times before hand (don't plan to just leave them with a bottle that night if breastfeeding and hasn't been tried and tested, it almost certainly won't work). I had to pump, so if BFing you need to make provision for that. And I was in tears just after the meal cos I NEEDED to get back to my baby!
I left DS2 at 3.5 months for 2 nights. Should have been with DH but he got called away unexpectedly with work so my mum took him. I pumped 72oz of milk for those 2 nights and he guzzled the lot and she had to rush out to buy formula! But he was absolutely fine, it was a great bonding experience for my mum who loved the one on one time and I didn't cry at all this time! (Though again, much pumping was required).
We have a wedding that I'd like to go to 2 months after DC3 is due. It will involve leaving her and travelling a few hours away and an overnight stay. Even though this is my 3rd there is still no way I can commit now. I don't know how she'll feed, how she'll settle with others, etc etc. So my RSVP will be an explanation with a 'completely understand if you need a definitive answer now, in which case it will be a thanks but no thanks, but if you have flex then we'd love to come so can we wait and see'.
Long and short... you have no way of knowing yet. Also, I am very fortunate to have family to help. A stranger is a different thing and I don't think I could leave any of my kids, even now, with a stranger overnight if they hadn't spent some time with them before. So I would very strongly recommend finding the person you want and 'testing' them out first and checking how they get on with your baby, how well they can settle them etc. Could get expensive fast.