Yep, you've got it.

The courtesy light does stay on for a few seconds, not long enough. Other devices like the Nav stay on for about 10 minutes. As you probably know, full shutdown (sleep mode) is about 16 minutes, but as far as I know that's all the devices doing their own shutdown modes. I don't believe there's a master snooze wire or anything like that

Again - the courtesy light solution is a step in the right direction, but I don't think it could supply enough power for twin DVD players for 10 minutes. I'm guessing, since my electronics isn't good enough to properly do the maths, but shooting from the hip, I'd say that would require a monster (even life-threatening capacitor) to augment it enough to deliver that amount of power for that period.

I think my first instinct, regarding a triggered timer solution is what's needed here.

Hoping somebody with better electronics know-how than me can sketch one out.