For a party, people need several days notice to plan whether to get off work, arrange childcare or find transportation. Six hours is OK if it is a "you were already invited, here's a reminder" message but not as a brand new event planned, much less telling you to invest money in the item.
I have had this sort of thing happen, but usually it is "Oh, yeah, Mom, so and so has a party tomorrow, here's the invite they gave me last week". In these cases, we had notice but my child failed to communicate it.
When other parents tell me the night before, I wonder if I was the backup invitee in case someone else didn't come or their child really begged to add us ... at which point, we're not their first choice and I won't go out of my way to attend.
For any professional or personal adult activity, I rarely join in something with that little notice unless it is "hey, I finally have Mom watching the kids, can you go out to X movie with me?"