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It depends on the site's current set up. Most of the changes will be found within 30 days of them being made if the site is not blocked in robots.txt.

So if I add my site to this same directories, press release sites plus I keep adding fresh blog post I will be ok????? You do not want to copy your competitors, you want to beat them. Based on the information you shared it is likely your competitors have many low quality back links which you do not want. You want to earn quality back links. You need people who independently choose to link to you because they like your content. You don't want links because you spammed a blog, paid for them or otherwise manipulated the system. Those links often do not offer any value at all, or are caught later and devalued leading to site owners to ask "why did my site lose it's rankings?" Fresh blog articles are good IF they target useful keywords AND the content is exceptionally well written. Fresh alone is definitely not good enough. How this online shops rank for so many keywords for every subdomain if they dont have any content on this subdomains? In order to possibly guess we would need the name of the site and the keywords they rank for. Then an analysis would need to be performed of the site, it's links, the keywords and so forth. If you wish to better understand SEO, I strongly recommend reading the Beginner's Guide to SEO. It is a short, outstanding booklet with a lot of accurate and helpful information.