I've been thinking about that.
In the Bible the number forty generally has to do with times of trial or testing. Perhaps discipline.
The rains fell forty days and nights during the flood.
The Israelites wandered the desert forty years.
Moses lay prostrate before God, fasting and praying, forty days on behalf of Israel.
Goliath taunted the armies of Israel forty days.
Jesus was in the wilderness, fasting and enduring temptation, forty days.
There are a couple of times that the aspect of suffering or trial doesn't seem to fit:
Moses was with God on Sinai forty days while he received the law.
David and Solomon each ruled Israel forty years.
I'm not sure what Christ's last forty days signifies. He walked among us in His glorified body. He must have been ready to move on. Short-timers syndrome. But I can't see why He would need to sacrifice yet more. Or go through anymore trial. Maybe it was related to his Kingly reign, as David reigned. Or perhaps it coincided with the initiation of the first Covenant when Moses spent forty days with God.
I don't know. And I have no application. It's just something I've been contemplating. If you have any insight, I would love to hear it.