Everyone has a different schedule on when to they do water changes. It really depends on your tank and how well the tank does between water changes. If after 1 week your tank looks good then maybe you could go 2 weeks between water changes. If you tank does good after weekly water changes that may work for you also. So it's really up to the person and how their tank is. Also the % of water changes that you do comes into play. Some people do small weekly water changes other do large month ones.
Your skimmer should help make your water better but shouldn't be something that is used to reduce water changes.