I just talked to the diving school The outcome:
- I will do the deep dive on day 1, instead of day 2 in the morning
- The last dive on day 2 will be with Nitrox and very shallow
- The last dive will also be earlier than usual, so that I finish at about 1 PM and have 18 hours between my dive and my flight
- If, for one reason or another, the last dive on day cannot be done that early, it will be moved to another day after my business trip
Sounds reasonable, and glad you discussed it with them. The issue of flying-after-diving is something that meshes nicely with what is taught in an AOW course, and it only makes sense to bring it up for discussion.
As you likely saw above, 18 hours is in line with what DAN suggests is reasonable:
"For multiple dives per day or multiple days of diving, a minimum preflight surface interval of 18 hours is suggested."