You'll need 1 trigger_multiple, 1 target_delay, 1 target_relay and change the func_static to a func_wall - this is how to do it without any scripting whatsoever.
Target the trigger_multiple to the target_delay.
Target the target_delay to the target_relay and to the func_wall.
Target the target_relay to the target delay.
Set the target_delay to have a wait value of however long you want it to switch on/off.
Set the trigger_multiple to have a wait value of -1 and place it either covering your entire map (so it will be triggered when the map starts and someone enters) or by placing it where a person will spawn every time (works fine for SP).
As you can see the target_delay will switch the func_wall but will also call the target_relay which will simply re-activate the target_delay so it toggles again and this loop will go on forever.
What you can do is simplify it all (if you know scripting) by running a script when the map starts which loops and toggles the func_wall indefinately but I always post entities first as it's there now and requires no extra programs.