A guy stuck his head into a barbershop and asked:

“How long before I can get a haircut?”.

The barber looked around the shop full of customers and said:

“About 2 hours.” The guy left.

A few days later the same guy stuck his head in the door and asked:

“How long before I can get a haircut?”.

The barber looked around at the shop and said:

“About 3 hours.” The guy left.

A week later the same elderly guy stuck his head in the shop and asked:

“How long before I can get a haircut?”