How long Google update the cached page

For my website, which creates 1 article per day, it took Google 10 days to update the cached page. Here is how I tested it. First, I created an article and then let Google cache that page. On the next day, I modified half of that page. Then, from there on, I check whether the cached page is updated by searching it every day using the following syntax.

KEYWORDS_TO_FIND_ARTICL  site:openwritings.net

On the top of the cached page, Google shows when that page was cached.