If I edit all my articles for SEO, will Google re-index my posts?
Google is continuously re-crawling your articles already, but when they see changes going on they will often increase crawl frequency to find out if there's anything new to be crawled.
and rank them better?
From the sound of it you're paying attention to some key on-page factors so I'd say yes, there's a good chance your articles will be ranked better after you published the changes. But don't get your hopes up, for competitive keywords it takes a lot more than just some fresh content to jump to a top 3 spot in the search engine result page (SERP). Backlinks still play a huge factor here.
If yes, how much time will Google take?
No one knows, time will tell. It can be a couple of days when you get linked to from a very authoritative website (they pass a lot of link authority). But it could also take a couple of weeks/months.
You can look at the Crawl Stats in Google Search Console to get a feeling for how many of your pages Google crawls on a daily basis. Still, that doesn't say that much. The only thing you can do is make all the adjustments to the content you had in mind (plus submit your XML sitemap in Google Search Console to make sure Google knows about all of your content) and make sure the content gets some fresh backlinks. Search engines will follow the links going to your website, hence speeding up the crawl process.
Do you recommend that I edit all the posts?
I would prioritize them. I hope you've done Keyword Research to figure out what keywords should be incorporated in what pages. If you have, then you also developed a feeling for what you could potentially gain. Prioritize based on potential, and work your way down the list.
As for keyword research and such: it's really important you research carefully what keywords are relevant to your pages. Don't worry about keyword density, that's an old concept. Instead, read up on Latent Semantic Indexing (LSI). LSI keywords are basically keywords which are strongly related. Not just in terms of singular and plural, but also in terms of topical relevance. So for instance when you have an article about someone getting fired, an LSI keyword may be 'severance pay'. Give this simple tool a try to get some quick ideas: http://lsigraph.com/.
It's kind of a broad question but I hope I answered your questions.