Ignoring the failed First attempt, and the fact that you even tried that here (nobody likes it, just FYI), I assumed that Deathwing was technically in hiding after the Enter the Dragonqueen events, where Dee-dub and Alexstrasza fought each other in Twilight Highlands.

So timeline, as I see it, would be:
-Deathwing begins Cataclysm.
-Deathwing summons Ragnaros into Mount Hyjal.
-Deathwing torches ALL THE THINGS (before Mt Hyjal, after, or both).
-Deathwing gets in tangle with Alex and goes into hiding to heal and pull other strings.
-Deathwing meets Thrall below Mount Hyjal (see online story).
-Deathwing comes to Wyrmrest Temple with entire Twilight Dragonflight to stop Thrall & Co.

The "goes into hiding" bit relies entirely on what Alex believes DW will do after their fight, though. There's no other text indicating this is what he's actually doing.

Also, the CMS is buggy on this site and there's a significant lag between comments being posted and them appearing. So 'firsts' mostly fail like yours did.

my question was actually how many years has he been torching it? Seriously doubt it was all in 1 yr.