Relinks should be as short as possible, but on the condition that a gemstore item that allows you to "vote" for what server you get linked to be able to be purchased an infinite amount of times, with each vote counting for 1 towards the server you want to be linked to. Nothing could ever go wrong with this system, it is undeniably sound in theory.
Otherwise 2 months is fine, short enough time for people to be comfortable and if you get a "bad link", it's over in 2 months. Lots of people voting for less than 2 months have either been the victim of, or contribute to the friendly term "bandwagonning" where they either stack the server or a server is left desolate cuz people wanna "win WvW" lol