All I know is the ding-ding goes off right before the flight attendants "prepare the cabin for landing" and do the final check.

BTW, when is it officially safe to recline after take off? They say "seat backs and tray tables must be up for take-off" but I presume after take off you can recline. Is the official answer when the dings occur and electronic devices are safe?

When I am on the redeye, as soon as we are high enough that I don't think we are going to end up on the ground in an uncontrolled fashion I put the seat back.