I take all aspects and changes to our sites very seriously, especially the Title tags & page content. I too adopted a Moz campaign and recently revamped our keywords to better target our product pages SEO. Analyze a Keyword is one of my favorite Moz tools. We have seen measurable improvements since that major update.
How Long to take effect? That depends on numerous variables; DA, Traffic, Links, Outside Advertising, etc... when I want faster results, I submit the updated page for indexing through Webmaster Tools.
Hope this helps
KJr