I removed some web pages from my site quite a while ago. When I searched for those pages in Google, of course, I could no longer find them.

I have now updated those web pages and re-added them to my site. How long does it take for Google to re-index those pages?

really depends..... I'm sure some members no more about this, but my guess is anywhere between now to 1 month?

on average, I think its about 2-3 weeks max.

Go into your logs and see how often Google has been indexing you up to this point. Chances are you can figure out the trend pretty easily by going back a half year or so. Some sites are indexed every day, others every 6 weeks or more. Google places pretty heavy emphasis on updated content. If it sees you changing things a few times, it will come around more often. Likewise, if it sees a trend of little or no change, it will decide you're not a priority.

The pages will be spidered as new, no matter if they where once indexed.

Say about 2 weeks. Depending on how often and how deep your site gets spidered.

<META NAME="revisit-after" content="X Days">

Replace X with your desired number.

that tag is meaningless, google crawls websites periodically based on how many quality links your website has incoming to it basically; more quality links, the more likely you will get crawled every 24-48 hours.

new pages can be added in right away after the crawl, until there re-ranking is another issue. At the moment googles trend is to index new pages quickly and you will only find them ranking under obscure terms until google calculates every factor in.
this factor seems to be a combination of your pagerank, age of links and just time.