Configure a timeout in web.config for a web service

Hello everybody,
I have a web service hosted in IIS 7.5.
The web service works fine.
I try to configure a timeout in the web.config, but I can't do it.
I tried in my web.config :

<Configuration><system.web><compilation debug="false" targetFramework="4.8" /><httpRuntime targetFramework="4.8" executionTimeout="10" /> <!-- 10 seconds --><sessionState timeout="2" /> <!-- 2 minutes --></system.web></Configuration>

and in the web service controller :

Thread.Sleep(180000) //3 minutes

I thought the execution would stop after 10 seconds but instead it stops after 1 minute, whatever I put in the "executionTimeout" and "timeout" parameters.
I have searched in IIS but impossible to find what this minute corresponds to.

Does someone have an idea ?

Thanks a lot in advance.

Eric.