Since on most servers reserving a wedding is highly competitive, I don't understand why anyone would risk their slot by starting late. Even if I hadn't read the instructions and known about the 20 minute limit, I still would have shown up early and started exactly on time. Their logic to the limit is so people's weddings don't get cut off due to another one starting. It makes sense - although I'm not saying the wedding system as a whole is good or bad.

I personally show up to ANY appointment thirty minutes early. A policy to live by for both serious and casual appointments, real life or not. Your boss and friends will respect you for your punctuality.