If the server is there, but you can't see details and you know the connection is correct, you can still enter it.
I had some delay after setting up my No-IP account.
I entered everything correctly in the SAMP client (hostname
ort), but the client couldn't get info about my server.
My ports were forwarded and all, because entering my WAN-IP instead of the hostname displayed the info correctly.
Even though I couldn't see my server when I used the hostname, I could still enter it properly, and play.
Several hours later, after exiting the client and opening it again, the hostname worked properly, without changing anything.