There are two ways to set a session timeout in ASP.NET.
First method:
Go to web.config file and add following script where sessionstate timeout is set to 60 seconds.
  1. <configuration>
  2. <system.web>
  3. <sessionState mode="InProc" cookieless="true" timeout="60"/>
  4. </sessionState>
  5. </system.web>
  6. </configuration>
Second method:
Go to global.asax file and write the code below. This code sets the current session Timeout to 60 seconds.
  1. void Session_Start(object sender, EventArgs e)
  2. {
  3. Session.Timeout = 60;
  4. }
Learn more about ASP.NET Session State here: Introduction to ASP.NET Sessions