OP here.
I agree. We constantly get 24 hours notice from DH sister inviting us to BDay parties or other kid celebrations.
She gets so offended and hurt if we can't make Saturday morning mimosas (90 minute drive one way) for Larla's birthday party when she tells us about it Friday at 4pm.

MIL got in a huge tizzy about it last weekend how we weren't supporting family. I am just like "lady, we have plans already, its less than 24 hours notice". MIL says "Well not everyone is a planner like you. Why punish Larla?"

Last month.

And expect them to show up? That window has passed. You need to give people at least a week's notice (assuming they are local). You can invite them today, but you can't expect that they will be able to attend.

A month or a couple weeks st the least. We have a social family and there are always things going on with them.

You can invite them, but keep your expectations low. Many people are busy and plan ahead.

That said, I think you need to invite now/no later than Thursday mid-day if you want people to show up on Saturday or Sunday.

ASAP!

Also, have zero expectations. These days people plan months in advance.

Assuming they’re local, I’d give them a month or so at least if it was somewhat important to me that they be there.

Let them know ASAP.

If you were having a party this Saturday, what is the latest you feel you could let them know and expect them to show up.