It's hard to say. Spiders regularly return to the web pages they index to look for changes. When changes occur, the index is updated to reflect the new information. However, the process of updating can take a while, depending upon how often the spiders make their rounds and then, how promptly the information they gather is added to the index. Don't waste your time with a search engine trying to find late-breaking news.
Search engines are the best means devised yet for searching the web.
On the down side, the sheer number of words indexed by search engines increases the likelihood that they will return hundreds of thousands of irrelevant responses to simple search requests. Remember, they will return documents in which your keyword appears only once. Search engines use selected software programs to search their indexes for matching keywords and phrases, presenting their findings to you in some kind of relevance ranking. Therefore, your search is going to be different on every engine you use. The difference may not be a lot, but it could be significant.