How to increase session timeout in ASP.NET MVC

Open the web.config file, then increase the value in minutes by using the time out attribute of SessionState element.

<system.web>   
    <sessionState timeout="300"></sessionState>
</system.web>

By default, the session timeout value is 20 minutes. Also in your case if you are using forms authentication, please check the timeout value.

<system.web>   
    <authentication mode="Forms">
      <forms loginUrl="~/Account/Login" protection="All" path="/" timeout="300" />
    </authentication>
</system.web>

Open IdentityConfig.cs, then change the value of the account logout time span that you want to change.

public class ApplicationUserManager : UserManager<CustomUser>
{
    public static ApplicationUserManager Create(IdentityFactoryOptions<ApplicationUserManager> options, IOwinContext context)
    {
        var manager = new ApplicationUserManager(new UserStore<ApplicationUser>(context.Get<ApplicationDbContext>()));
        // Configure user lockout defaults
        manager.UserLockoutEnabledByDefault = true;
        manager.DefaultAccountLockoutTimeSpan = TimeSpan.FromDays(1);
        manager.MaxFailedAccessAttemptsBeforeLockout = 5;
        return manager;
    }
}