Has anyone figure out how to get the achievement? I can't find any info on this
If you don't mind cheating there is a saved game you can download over at steamcheeves.
"Savegame here. Disable Steam Cloud for Revenge of the Titans and after that extract the contents of the archive into C:\Users\YOURUSERNAME\.
Start game, make sure the top banner asks if you're Bilbo and if it does, start the bonus level with previous progress (it will ask you if you want to do that). Again, as with any save games, back up your own files before doing this. They're located inSteam\userdata\YOURID\93200\remote if you used Steam Cloud with the game before. The loaded game should not require any player interaction, just fast forward the time.