Why is there a 15 minute waiting period before allowing users to accept an answer on Stack Exchange?
It started here:
The rationale is that if people are accepting answers within minutes or even seconds (no joke), they haven't even had time to properly evaluate or test the answer. The community felt (and I agreed) that some users were just accepting the first answer that was submitted even if it was wrong or sub-par.
15 minutes was decided on as the minimum amount of time it would take to receive a healthy number of submissions and actually read/test/think about the answers provided.