Nora dearest, I had initially thought the things could be related, but apparently not! So far we have:
Three different breeding times (4 hours, 8 hours, 12 hours all with double gold).
Different flames for hatching dragons.
Different capacities on crucible (first upgrade: 25 and 50) and silo (250 and 500).
Bleh. At least I got 4 hours breeding time.