Nice question - good challenge!
OK, here's one way you could do it by scripting... I wouldn't try it with time outs or chapter points, because you don't get a reliable counter that way.
First off, set up a script which sets GPRM0 to be a counter, move a value of 0 into that counter and exit the script (which will be a pre-script when we use it):
GPRM Mode GPRM0 to Counter
mov GPRM0, 0
Exit Prescript
Now, attach that to your menu with the button on that needs to be activated.
For the button which has to be activated within five seconds, set it to first go to a script which checks the value in GPRM0. If it is equal to or less than 5, the target will play:
Jump Trackname If(GPRM0 <= 5)
Jump menu2
Where Trackname' is the intended target if the button is activated in time.
On menu 2 you can either make a duplicate of menu 1 without the hidden feature, or you can give a message and send them back to menu 1. When you arrive at menu 1 the counter will reset to zero and the user will have another five seconds to get the button activated.
GPRM counters in DVDSP increment by 1 second at a time when activated. Setting a counter into a pre-script means that the counter will start as soon as the menu is called.
For what it's worth, five seconds is very short. If your user has to first take in what the menu is doing, then navigate to a 'start' button, then press 'down' three times - it's a big ask!
You will also need to set the menu navigation up carefully, making sure that the navigation from the 'start' button goes to a stack of hidden buttons, and that navigation from these only goes to the target if the down arrow is used. Any other direction should take you back out to a visible menu button, IMO.
You can stack the hidden buttons underneath a visible one to prevent computer users 'mousing' over them, but remember the order of the stack is the last button drawn goes on top of the others by default. Therefore you need to start off with the last button in the stack OR alter the order of the button arrangements using the 'arrange' feature in the menu editor.
Its going to be a challenge for you (or anyone) to get this right, but it sounds cool to do!
Hope this helps 🙂