A joke or brain teaser about friendship

"Do you believe I can know what time it is by playing the piano?" A man asked his friend.

"Stop joking!" His friend answered suspiciously. "Then I'll try to show it to you." Then he sat at the piano and began to play the March.

A few seconds later, there was a hammering sound on the wall, and an angry voice shouted, "Hey, you son of a bitch, do you know it's three o'clock in the morning! ! "