I just got my 44 hr wait time on my 3rd attempt for a diamond. I used a level 10 leaf lion in the left and a level 9 palmwing on the right. The previous two attempts they were both level 9. I'm currently level 16.
I also play dragon story(level 39) and still have not bred a diamond (40+ attempts). I figured that I would try for the diamond early before the variety of monsters increased to the point of too many possible outcomes.