I bred a Dolphin Dragon from two Sea Dragons (one 12th level and one 6th). I was trying to do a quick dragon breeding at the time... instead of 30 seconds, it was around 14 hours.
Dolphin was not in the breeding event list at the time.

@blijf-an-oniem Always check possible results before starting a breeding. Many things changed after breeding reborn. The only guaranteed short breeding is Terra + Terra unstared now.