Skin infections start to clear up within a couple days after taking antibiotics for the skin infection.
The skin infection should fully go away and heal within 10 days after you begin taking antibiotics.
I'm assuming you're asking about a skin infection called Cellulitis which is a bacterial infection of the skin and the tissues that are beneath the skin.
Staphylococcus and Streptococcus are the two bacteria that cause Cellulitis.
If your skin infection isn't going way within 10 days while on antibiotics you need to see a doctor again since the skin infection could be more severe.