As soon as possible.
It took my foster father 20
(partly because he was born in Montreal, and not Catholic. In those days your birth was not registered if you were not Catholic. So it took awhile to prove he was born)
years to become a US citizen and he was married to an American and has been working the US for that time (he was Canadian).
(Oh, and nearly $50,000)
I do not know what Mr. Cruz took so long, that does not diminish him as far as I am concerned.