I added those name servers to my domain name registrarīs records, about 20 hours ago. However, I still cannot start an SSH session to them, nor do they resolve yet.
Does it matter which one of the domains is my primary domain?
It should not matter which domain is your primary. Try connecting to the IP address instead of the domain. If that doesn't work, feel free to send me a Private Message with your account details (IP, username).