How long does it take google to unindex pages

If you have lots of pages that lose relevance, best to use a no robot tag?

[Onders]

The nature of a website I'm involved in means that a lot of pages lose relevancy quickly and need to be removed. Is it best to have them all indexed and wait till they get unindexed (how long does this take?) when I remove the link to them, or should I make all the pages unindexable.

If everything is indexed then people will find old pages which is a bit of a problem - and although I could put some standard text on the page, I'm worried this may lead to duplication problems..

Any ideas on timescale for unindexing?

Thanks

[Vadim]

Google has an immediate removal tool. You will find the link at
[google.com...]

Basically you first use robots.txt and then submit the link for the immediate removing (one two day as far as I remember)

If you do not use this tool the page may stay in the index for months.

However, I feel it would be better to reuse the same URLs, if it is possible to make so that they have the realted content.

Naturally you always may make so that the pages are never indexed if use NOINDEX meta tag.
<META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">

Vadim