Don't Google it, you cheaters.

A couple lives in city A and the wife works in city B (the husband works at home). Every day the wife takes the bus at 4 PM back from city B to city A and the husband comes to pick her at the bus station and they go home (it is unknown when she gets to city A but it is in the same time every day).

The husband is so good in timing this that he knows exactly when to leave home in order to pick his wife at the exact time that she gets off the bus in city A.

One day the wife took the bus at 3 instead of 4 and as a consequence got to city A an hour before the regular time. It was a nice day so she decided not to call her husband but to start walking in the direction of their house.

Her husband didn’t know anything about this and left at his regular time to pick her up. On the way to the bus station he saw her, picked her up and they both returned home 20 minutes earlier than usual.

The question is: How long did the wife walk before she was picked up?