server timeout not working properly

Question

=> If I want to set the timeout 450 min then what can I do in server and application?

 

=> already set 450 min session timeout in my Global.asax file in the project then it's necessary to set time in web.config file?

 

=> Once I already setup SESSION TIME in the IIS session management in server setting but didn't work and if I'm setting the time then it will work for 1 or 2 days after that, session time reset as default so what can I do for this hurdle, please help me out in this.

 

thanks in advanced