Guild Wars 2

Are they a permanent addition to the Trading Company? I just wanna know how long I have to get all three.

More importantly, how does this affect the height of the bar that’s set for Legendary?

Duration wise they are almost certainly permanent. Typically limited edition items have a duration listed with them on the trading post. Most, if not all, of the complete armor sets have been permanent additions – Flamekissed, Aetherblade, Phalanx, etc.