How long, and where??

[CascadeRX]

How long does it take before Atani starts to show that she's pregnant also where do I find Byvernia as well?

 

[Alypia]

I can't speak to your mare-iage, but as far as the angry bunny goes...

From my experience, Byvernia shows up in the southern and southwestern Foothills - the area outlined in red on the map. The tile in the dotted outline might be a valid spawn, but I've never seen her there.