On average Google will update your search result title and descriptions within one week. Often they will be updated even faster, within one or two days.
Ultra SEO supports the title, description, author and keywords meta tags.
These are helpful suggestions on how long your title and description should be. You can go over the limit, but Google may truncate some of your text.
In Shopify 1, they are near the top of the page for each product / collection / blog detail view. In Shopify 2, they are in a drop down menu called "Apps" near the top-right of the page for each product / collection / blog detail view.
Relevant meta tags help quite a bit with page rankings. We have seen a majority of our users page rankings increase shortly after installing and using Ultra SEO. However, this is not something that we or anyone can guarantee. Page rankings are determined by Google.
The best practice for the title tag is to have it briefly describe the page it is on. Remember that the title tag is rather short. Because of this it is best to not include the name of your shop in all title tags. The name of your shop should be in the shop title tag and other title tags should specifically describe the page they are on in a brief fashion.
The best practice for the description tag is to have it naturally describe the page that it is on while staying within the character limits. Avoid using keywords lists here. Keywords are good if they are naturally included in the description.
Some search engines use the keywords tag and some do not. Therefore use of this tag is completely optional. Leaving it blank will cause it to not appear in your code. If you would like to use it list keywords separated by commas.
The author tag is mainly used by blogs to indicate who wrote a blog entry. It can be used elsewhere if desired and is also safe to leave empty.