how long your keyword rank first page

6 months ago i created 10 website 50% of them rank first page for 3-4 months then disappeared in Google never come back

You have to keep posting articles and back-links to your main url and inner pages  to keep up with completion . Content publishing it's not set and forget business . Good luck !

Yeah you either got slapped or stopped building links and saw your rankings drop b/c of that.  I don't think link velocity as important as some people say, but you can't straight up stop once you achieve the rankings you want. 

Depends on the KW. Some I have spammed and forgot about, still there 4 months later in top 3. Others I lose after 2-3 days.

it weird  some keyword i cant rank with GSA SER but some keyword high competition 100k exact search i still rank first page  )