Who knows what time this joke is?

The two boys are camping in the backyard. When they didn't know the time, the first boy said to the second boy, "Start singing loudly." "What's the use of that?" The second boy said. "Just do it," insisted the first one. Both boys sang loudly and sang at the top of their lungs. After a while, a neighbor opened the window and shouted, "Keep your voice down! Don't you know it's three in the morning? " What time is it now? Two boys are camping in the backyard. They don't know what time it is at night. So, one boy said to another boy, "Let's start singing loudly." "Then you know the time?" The second boy asked. "Sing." The first insisted. The two children began to sing loudly. After a while, a neighbor opened the window and shouted, "Keep your voice down! Don't you know it's three in the morning? "