I assume you are correct in your supposition that it depends on what category has been reported.
Last weekend There were a lot of spamming posts (re. poetry) that I reported as Advertising/Other. I find it hard to believe that less than two others did likewise, but the posts remained in place until Tuesday morning. On the other hand, about 4 or 5 months ago there was a really offensive and abusive post that I reported and it disappeared immediately so I assume I was the last one needed to make up the necessary minimum.
I don't agree with reporting something as being what it isn't. For example, the puerile postings of an immature child can hardly be called 'abusive'. I report them as 'Other' in order to bring them to the attention of the moderators (as per site instructions).
In my opinion, the current moderators should be sacked because they do B-all when the boss isn't around. (i.e. Weekends and Bank Holidays)