No, your SSH key can't be broken in a few hours if you choose a strong passphrase. I read the web page you quoted, and it is just bad writing that leaves a mistaken impression. The statement there is inartfully phrased. The website claims:
An SSH key passphrase is a secondary form of security that gives you a little time when your keys are stolen. If your RSA key has a strong passphrase, it might take your attacker a few hours to guess by brute force. That extra time should be enough to log in to any computers you have an account on, delete your old key from the .ssh/authorized_keys file, and add a new key.
That's phrased in a pretty confusing way. I suspect what they mean to say is that a good passphrase will take at least several hours to crack. In fact, a strong passphrase will take a lot longer than that to crack; probably days or years, or longer, depending upon how strong your passphrase is.
Because of poor phrasing, this web page might leave the impression that even if you choose a strong passphrase, an attacker could still recover your SSH key in at most a few hours. That is not correct. If you have a strong passphrase, it will take a long time for an attacker to recover your SSH private key.
Someone with permission to edit the web page should fix it to correct the confusing phrasing.