PvZ Garden Warfare gives you three days to play the game. The timer doesn't start until you click play for the first time. Kingdoms of Amalur: Reckoning provides you with 48 hours of game time. This also doesn't start until you click play for the first time.
Just keep in mind that these games are only available for a limited time and once that time is up, you won't be able to start the games unless you purchase them.
