B717 APU question?
 

In case you turn off the APU by mistake, does this one has a protection to delay the cut off so you can return the switch to the on position and that way solve the mistake?

Do not think so.

I wouldn't trust it anyway. Saw a line of palm trees go up when the APU restarted with a 'spit' of about 150 feet on the next door A/C. Fire brigade came over to the two MD types to figure out who did the fiery deed.

My MD87's right cowl was clean, reasonably soot free. The 717 alongside was missing paint and soot from their cowl.