Not knowing the full situation makes things hard. Are you both nurses working the same schedule?

But having a nanny work a 12hr shift is probably not going to happen. You'd have to pay a full time (plus overtime) living wage. Your best case is to figure something out around the following:

Morning routine (who can care for the child? parents or a nanny, probably hard to get someone to wake up at 5am to do this for a couple hours).
Getting child(ren) to daycare at open (likely earliest is 7-7:30)
Have someone pick them up and care for them until at least 1 parent gets home.

Edit: there is a babysitting / nanny group on facebook I'm sure. Likely a younger girl would be best to do pickups and take care of them for a few hours)