Every party has a threshold for when it’s socially acceptable to be late. If your friend has a daytime birthday party from 4 to 8 and you show up at 7:30, that’s a tad bit impolite. Some might say it’s also disrespectful to show up to that event at 3:40, and I’m inclined to agree. But let’s say it’s not a typical party with a sizable group of attendees…let’s say it’s a modest gathering of four friends who are hanging out to celebrate a birthday from 4 to 8 PM. In that case, it wouldn’t be kind to show up 1.5 or 2 hours late. When it comes to kids’ birthday parties, it’s definitely expected that you show up on time, especially if there are activities planned throughout the day. If you have to miss 75% of a birthday party, you might as well not come.