I suspect that the sleep command will swallow the keypress. Passing it
on to the menu somehow would be one possible avenue of attack here,
though possibly counterintuitive; I'm not sure that I expect e.g.
pressing Enter at the hiddenmenu delay to effectively bypass showing the
menu and immediately boot the first entry. So experiment and be
careful.
I suspect that the sleep command will swallow the keypress. Passing it
on to the menu somehow would be one possible avenue of attack here,
though possibly counterintuitive; I'm not sure that I expect e.g.
pressing Enter at the hiddenmenu delay to effectively bypass showing the
menu and immediately boot the first entry. So experiment and be
careful.