Oracle Life Mystery Delay Affliction

[Yonman]

Delay Affliction (Su): Once per day as an immediate action, whenever you fail a saving throw against a disease or poison, you may ignore its effects for 1 hour per level. At 7th and 15th level, you can use this ability one additional time per day.

Since this is an immediate action, does the PC take ability damage/drain on the initial saving throw? Or does everything, whether or not you take damage, get nullified for an hour?

[Mysterious Stranger]

An Immediate action can be used at any time. That should mean you can use it after the saving throw, but before the effects are determined.

Some poisons can potentially kill you if you fail your save. This ability would be worthless against those if you cannot use it after the save, but before the effects takes place.

[Pizza Lord]

I would say that based on the timing of action and how it's written, that you are protected from the damage when you fail the save and choose to use the ability. It's still there, meaning when the duration wears off, you will receive the penalties or damage or whatever effect (unconscious) the poison or disease would have caused on the initial failure (unless you had it removed or neutralized before then).

It would also mean you can't cure any ability damage or drain, since it's not technically there (just in case your GM had rolled it already and was just 'holding it off').

[Azothath]

some spells
→delay disease:C2 ARG 5/1/2012
→delay pain:E2 Ult Mag 5/10/2011
→delay poison:C2 CRB 8/1/2009

→Oracle Life Mystery APG 8/1/2010
Delay Affliction (Su). The text seems pretty clear given delay poison above. Afflictions are; Corruptions, Curses, Diseases, Drugs, Madnesses, Poisons. They're mixed with Hazards (Haunts, Traps).
HOPEFULLY the player speaks up before the damage is rolled or as it is being totalled. Most GMs informed in a reasonable time (like within a minute of the event but before other significant actions occur in the game) would say "just ignore the damage" and reroll it later otherwise stick with the damage done and ignore any more effects from that affliction for the 'time out'. Delay Affliction doesn't cure/heal or nullify any damage. It simply creates a time period where new effects for that specific affliction cannot manifest/be applied to the character.