Tarot cards last 3 hours - the effects of the cards may cycle on and off during the 3 hours
If the Tarot card has an effect when it expires - you must be at sea with provisions and no disasters.
Tarot cards from nobles cost $1000 Ducats
Tarot cards can be player made with the Alchemy skill, found in dungeons, or from Nobles
-Abbye
Sources:
http://unchartedwaters.wikia.com/wiki/Tarot_cards
http://unchartedwaters.olous.com/tips-guides/320