I have the same probleme too. I went to https://www.dynadot.com/account/domain/server/list.html then I clicked on "Register a domain name server" then filled the IP address out, but still not working it's been more than 24 hours.
I don't see what you mean here: https://www.dynadot.com/community/help/question.html?aid=87
By "remember to configure your name servers with the corresponding 'A' records." Which A record are you talking about? I'm expecting that ns.mydomain.com will point to myIP then I'll configure records on my own server.
I use name.com, it's just a 1 step and things are done.