I have developed a tactic with people like this (unfortunately, this is mostly female friends and my wife... ) If we need to leave at 9am, I tell them that we need to leave at 8:45am. Then most of the time we can actually leave by 9am. My wife quickly caught on to this, but realized that it was quite effective which leads to conversations like this: "What time are we leaving tomorrow?" "9am" "So I need to think we are leaving at 8:45am"
The caption is important. Before I read that I was thinking of the scorch marks left by the ancient Pompeii disaster.