I think the reason Abyssea NMs had their timers reduced was because of the incredibly high demand for them and the fact Abyssea is on (some sort of) a time Limit.

However, I wouldn't mind a maximum cap imposed... Camped Bonnacon for ~3 hours the other day, popped, TH11 on, And my reward was a buffalo meat. I hate this game some days.

I don't think reducing the spawn timer for every NM universally would be a good idea, But i do agree some cap should be placed.