noindex meta tag - delayed effect?

It depends; I have experienced about one week delay when changing titles, etc., but if you wish Google to remove some of your pages from SERPS, it may not happen altogether. For example, I accidentally did let Google to index my duplicate test site; Google started to direct visitors into there too and I got a fucking mess dealing with it. All this despite the fact that the site was maybe a day or so for Google to index until I forbid it, but Google didn't listen. So, I did what I should have done at the first place; I did put the whole site under password.

So, long story to short; Google may not ever obey your wish. As it is a wish.

Looks pretty much it's the situation. Pretty annoying.

Advice for others: use noindex for tag / category pagination right from the start. Those pages don't have unique pages anyway, they will be treated as duplicate content.