Yes. That is very common and completely natural.
Both are correct. In conversation, people often leave out horas if the meaning is obvious.
By itself, São nove horas could mean either 9 in the morning or 9 at night. If you want to be specific, add a time-of-day expression:
These are very common in Brazilian Portuguese.
São has a nasal sound, which is one of the trickier parts for English speakers.
A rough guide:
So são is roughly like sowng without a clear final g, but nasalized.
The exact Brazilian pronunciation is approximately /sɐ̃w̃/.
Yes, the h in horas is silent.
So horas sounds roughly like:
In Brazilian Portuguese, the r in the middle is usually a tapped sound, somewhat like the quick tt in American English butter.
So:
In Brazilian Portuguese, nove is usually pronounced roughly like:
The final e often sounds like ee in many Brazilian accents.
So:
Not always. São nove horas is correct and natural, but in everyday speech people often shorten it.
Common versions:
So the full version is fine, but shorter versions are also very common.