This is only my opinion, but I believe the wasteland can be more lax.
There isnt really a line in the sand. Is the info the thread still relevant? Is it outdated? It should still be relevant, and not outdated. Examples would be, right now posting in a topic that pertains to something from episode 13 is likely outdated and therefore would be considered necroposting. Posting in a thread about the Reborn League which no longer exists would no longer be relevant.
My general rule of thumb for time if you have to have one is if the last post was about 3 weeks ago or more. This obviously varies for the topic at hand. It would be much shorter in a bug reporting thread, opposed to a thread likely to be found in Reborn City.
But it really comes back to Is it relevant? And is it not outdated?