From Screamscape
http://www.screamscape.com/html/disney_s_california_adventure.htm
http://www.screamscape.com/html/disney_s_california_adventure.htm
General Park News - (2/11/13) FastPass attractions at Disneyland and California Adventure have begun putting up signs to notify guests that they will begin to enforce the 1-hour window printed on the FastPass tickets. We saw this go into effect last year at Walt Disney World as well, as an anticipated move about a year-ahead of the test launch of FastPass+.
Previously, one could get a FastPass ticket for 1pm to 2pm, but simply hold onto it and come back at any point later in the day and still use it, even though this was never the original intention of the system. I don’t know if this is a sign that the Disneyland Resort will also launch FastPass+ in about a year for Summer 2014 or not, or if this is just their way to trying to apply the same set of rules to all the parks in the US. Time will tell, but consider yourself warned that when it comes to FastPass tickets, you use them or you lose them from now on.