Thanks and glad that you like them. You know me, I like to credit members because the guides belong to us all - the community and great to see everyone pitching in.
Yes there are 6 possible breeds for Dark + Earth (listed under Dark or Earth creatures chapters in Creatures Guide) and those 3 are the common ones. Dusk Ox is the only one with the same breeding time. Wish me luck haha. Just wish the fails arent soooooo loooong lol.