Short Answer:
1 Day to 4 weeks
Long Answer:
This is really going to depend on your site and how popular you are. You really do not need to have a ton of visitors everyday to be popular in Google’s eyes. There are things that you can do to help get your pages re-indexed. Let’s talk about some of the things that you can do.
If you are trying to get a single page re-indexed you could just add a link to that page on the main page of your site or add a post to your blog with a like back to that page. You can also just get more links pointing to that page via posting articles on other sites or article directories. Article directories like Ezine Articles normally get crawled by Google very often. If you get a link on Ezine that points to your page you need re-indexed you will almost always get it re-indexed.
Great blog. I enjoy the educational stuff on search engine optimization.