He think that the time out begins when the child is calm and quiet on the chair.

From the point of quietness, the time begins.

If in that time the child starts to play up or moves from the spot, the time is restarted until calmness is resumed.

I've just ended it because I've had enough and don't see any benefit in allowing it continue that long. However she did not sit quiet for the 5 minutes at all.

She's now sitting quietly eating her lunch. She apologized for her original bad behaviour.

I now see that DP needs to be seriously counseled and educated on the pro's and con's of time out.