Q:

Why can't I immediately self-answer as a community wiki?

Why is it not possible to self-answer your own question immediately while marking it as community wiki?
As I understand it, with a community wiki answer you won't get any points out of it, and it's thus almost guaranteed that this kind of answer won't be abusing (in whatever way it's possible) Stack Overflow itself.
Also, the rationale for restricting almost everything to users with a low score, is to avoid abuse to the system in the first place. Thus, I don't get it. I'd be willing to post an answer that I spent a good chunk of time looking for, even without gaining any points for it: only for the good of others interested out there. Yet I can't do it until 8 hours are passed.

A:

Have a look at this question as for why self-answers within 8 hours are not allowed for low-rep users: Minimum reputation for answering your own question should be higher than what is needed to ask. This is all about preventing non-answers, and it has nothing to do with community wiki, so it's quite correct that you have to wait these 8 hours.
So just compose your answer right now, and submit it in 8 hours without making it community wiki – that may even give you some reputation, and next time you won't have to wait 8 hours. You have two possibilities here: either leave a browser tab open with your completed answer, or rely on the draft that will be saved after 45 seconds. However, for the latter option note that the draft will be cleared if you post other answers in the meantime.

