This is possible using any firmware.  Be sure that your router’s settings are reflected in the control center.

Click Modify Hotspot Data & Settings –  SPLASH PAGE SETTINGS  and change the Internal Login/Logout URL Set: to custom.

Then enter the network address in the internal login/logout fields. Make sure that you keep the format for each field according to your firmware, for example for DDWRT:

http://#.#.#.#:3990/prelogin

http://#.#.#.#:3990/logoff

The same goes for your router, make sure that you keep the same format for the ip address field for example, DDwrt #.#.#.#/24.

 

customnetwork

 

The popup window will automatically point to the custom ip network for users to logout.

Note: when redirecting users after successful login there is no popup window, so you should set a low idle timeout value or advise them what link to visit for logging out.