"It is the second hour."
Translation:Secunda hora est.
One thing that is not explained in all these examples is what is meant by "the first hour", "the second hour", and so forth.
The ancient Romans divided the daylight period into twelve hours, so, regardless of the season, the first hour always began at dawn, and the twelfth hour always ended at dusk.
We count the hours differently nowadays, and "prima hora" is now used to mean "one o'clock", as it is in any modern language.
A quick search of the classical authors finds about a dozen instances of "secunda hora" or "hora secunda" and none of "hora altera" or "altera hora".
I bow to usage! Although, it does look like Martial Epigrammata 4.81 uses "altera" to refer to the second hour of the day. That is the only pop I got on a PHI proximity search, though. But considering your work, I'll prefer "secunda" in the future.