То есть
When he had seen his wife off the station, he returned home as he hadn't to be at the airport bla-bla...
Это неправильно?...

Неправильно had seen his wife off the station. Он сделал что? saw his wife off Где? at the station.

Я постараюсь объяснить: всё это случилось в прошлом: (1) он проводил жену на поезд (2) он вернулся домой (так как...). Важным во всем этом является то, что (1) случилось перед (2) и, главное, что (2) было сделано только тогда, когда (1) закончилось.

When saw his wife off the station, he returned home as he hadn't to be at the airport at 10.00
Так?

Нет. When he saw his wife off AT the station, he returned home because he DIDN'T NEED TO BE at the airport UNTIL (LATER THAT DAY) at 10:00.

Oh, I think I got it. His wife had a flight let's say at 2 pm, and he also had a flight at 11 pm. So dropped her off at the airport and returned home because it didn't make sense for him to stay at the airport and wait for his flight that was later on the same day. Does it sound right?

Exactly!

Uly, can we say: When he SAW his wife off at the station....?
If yes, how does it change the meaning?

If you use WHEN, you’re going to talk about something that happened WHILE you were still at the station with your wife.

Ok, let me make sure I got it right:
1. When he had dropped his wife off at the station... means he left the station when the next action happened.

2. When he dropped his wife off at the station... means he was present at the station when the next action happened.

Did I get it right?

Correct

cool, thanks!

👍🏼😉