For me, about 1971.
Got caught in the aftermath of an ice storm, catching a Continental flight STL-BOS for college, and our normal 2-hour drive to STL from rural Illinois took almost 3 hours on the slippery roads. Dashed to the counter about 2 minutes before scheduled departure, and asked them to let the gate know we were on the way down. The aircraft had just barely started pushback, and came back for me.
No long security procedures in those days, of course.
My dad got an admonitory letter from Continental a week later, telling us it cost $20,000 an hour (1971 $$) to hold an aircraft that way. Good life lesson - I've always allowed an extra 60-90 minutes ever since, just in case.