How fast does it take for a substance to be absorbed thru the skin?

For instance, how long would it take for acne treatments to be absorbed and effectively used by the skin? I've heard it takes about 15 minutes for the skin to fully absorb something, but I am not sure about that and cannot find anything really on the internet. Thanks!

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).