You say to your spectators "Name ANY card I will find it in one minute!" One of the spectators names a card (free choice, no force of any kind).
Next, you take out the cards from the box which has been sitting on the table the entire time. You openly spread the deck face up and point to their card stating "I found your card!" Unfortunately, your spectators are not impressed... so you show that each card in the deck has different time imprinted on the back.
When the spectators card is turned over it shows exactly one minute!