Sorry was Wrath to Cata is what I meant and seems it was five years from the start of Wrath (when Cata hit Arthas was dead for 3 years).
From Cata to Legion was 4 years roughly.
While it's not 100% accurate it's a decent gauge using the books / ingame lore: http://wowwiki.wikia.com/wiki/Timeline_(unofficial)
For anyone interested in actual (real life) dates related to WoW and certain events: http://wowwiki.wikia.com/wiki/Timeli...d_of_Warcraft) -- Including the first legendary that was removed from the game because it was in by accident. (for those that remember). Looks like it includes things like commercials, certain memes, etc.