Keywords in meta descriptions are most likely ignored. Meta description may be used when displaying search results as a short desciption of your site there.
Google updates itself your site from time to time. Frequency depends on your own site update frequency and site relevance - not exclusively, but these are main factors.
The more often your site content changes the more likely it is that Google increases update frequency. Google Bots is adjusting update frequency to nearly fit your update frequency resulting in "fresh" results but not updating much more than necessary.
You can create a sitemap.xml and define the update frequency for a specific URL, so it may be more likely Google Bot revisits your site on this URL at this time to refresh data. I assume Google Bot just takes this info for initial update frequency as an entry point for the adjusting alg described above.