Adorable! Congrats!
I'd give it till the end of day 23 and then if there's no internal pip I'd go in through the air cell just to verify no movement and then do the eggtopsy.
You'll get it. The 1588 is a good bator, and once you tweak the humidity and all, you should have better results. Shipped eggs will always be a risk though.
I highly suggest a hygrometer for guidance, but I put more stock in watching the air cells to really know how to adjust the hudmidity.
Sorry to hear about the pony. Hope she pulls through. Congrats on the eggs!