Based on this thread in the Rogue community:
Cataclysm Mechanics Testing
and from several trinkets I've looked up while working on updating the Item Cache for Rawr, it would seem that Cata standarized most trinket ICD. There are a few (mostly tanking trinkets) that don't follow these new rules, but:
Trinkets with On Effect procs: ICD = 5 times the length of the Duration
Trinkets with On Use: ICD = 6 times the length of the Duration.
This means a trinket such as Left Eye of Rahj has a 10 second duration on equip proc, and a 50 second cooldown.
Key to the Endless Chamber lasts for 15 seconds on equipped proc, and has a 75 second ICD.
While Unsolvable Riddle which has a 20 second duration on use effect, has a 120 sec (2 minute) cooldown. I hope this helps with the trinket modeling. Took me a while to make sure all of the trinkets in Cata where working like this when I was updating Rawr's data cache.