Breathing pure O² on the surface after dives will have benefits in off gassing, with an EANX 32 or 36 the effect would be negligable. Regarding surface interval and flying. Typical cabin pressure is at between 6000-8000ft (that in itself is already a big variance), which means your absolute pressure is reduced by about 20-25%. That's the same as if ascending in a very short time span, the last 5-6 m (20ft) of a dive. This obviously has an impact on off gassing and DCS risk, you will create bubbels in your body.
The problem is that just like with a normal ascend of a dive, there are a lot of variables :
- The kind of dive you were doing (a shallow recreational dive vs a deep technical dive).
- The number of dives you've been doing (affecting the ongassing of your slow tissues)... liveaboard with 4 dives a day for 6 days, 1 big trimix dive or just 1 recreational dive.
- What gas you were breathing (helium for example of gasses much faster than air, but is typically used on dives with bigger ongassing/exposure)
- What deco/ascend strategy was used on dives (did you just ascend, did you do a deco dive and where breathing for example O² for the last part of ascend/on the boat)
- Finally and this is really the BIG ONE: what's your body like???
The final one is very important. There have been DAN studies where in a very controlled environment they let people ascend the same profile and are then checked on bubbles immediately post dive. It seems there are people who are "super bubble makers" and there are people who make not a lot of bubbles. Since stepping on a long haul flight is basically as if you are ascending on a dive... this will probably also generate different level of bubbles based on what kind of body you have.
Below is very anecdotal but aligns a bit with this.
I've got a good friend of mine who is a technical dive instructor, who because of circumstances, did a deep technical dive (90m+ 2 h deco) and literally stepped on the plane with his hair still wet (less than 3 h surface interval), without any issues. On the same side I've witnessed a diver getting a hit on a small plane flying back from one of the Atols to the capital of the Maladives, prior to connecting to a long haul flight... this DCS hit after 30 h surface interval.
So that's a big gap... between 3 hours no hit and 30 hours with a hit.. different people, different profiles. In the end it makes sense to use this 24h interval... better safe than sorry no? Specially since the risk and cost involved if your long haul flight has to deviate and make an emergency landing, because you took a "calculated risk"...
Still, for me I vary between 12 and 24 hours depending. I know my body, I've done a LOT of deco dives, and some very aggressive, so I have some anecdotal evidence how my body reacts to ascends. If I'm doing a deep technical dive which means only 1 dive a day, trimix, deco gasses, then the interval for flying will be shorter... if I'm just coming back from a liveaboard, doing loads of recreational dives... well you can be very sure I'm taking those 24 hours!
My 2 cents of course and all anecdotal.