This is a really interesting aspect of this discussion cause there is actually a possibility that a user can make a post that contains borrowed content but actually forgot to add the link immediately, or actually wanted to make the post first and then arrange the link(s) for a few minutes and then add them subsequently, but within that time another user could immediately discover that such post contains information that does not originally belong to the OP and archive such post as having plagiarised content.

I believe in such situations, the moderators would basically just handle the issue logically, since there is no rule on the amount of time for one to edit a message and add necessary links, they will just apply common wisdom in such a scenario, if the user actually edited the post within a day or two when no open reports have actually been made against the user, then we can assume it was all just a mistake and that the user forgot to add the link to the source, then again, if the user adds a link after an open report has already been made against the user and he claims to have actually forgotten to add the source, there is no way to know if such person is telling the truth, and it could be referred to as the user being malicious or trying to cheat, thus the moderators I think would actually decide the case on things such as: the reputation of the user, if that is actually the only case of plagiarism found in the users profile, is such a user one who makes shitposts with zero quality just to earn some pocket money, what contributions does such user have to the community, etc, I believe after a round up of all these, the moderators can easily decide if the user deserves a ban or not.