"Hello, what time is it?"
Translation:Dia duit, cén t-am é?
There is an explanation of the t- prefix included in the Tips & Notes under the Date & Time skill:
Words beginning with vowels
If a masculine singular noun starts with a vowel, a t- is added at the start of the word after the definite article an (for example, am "time", an t-am "the time"; uisce "water", an t-uisce "the water"). A hyphen is placed between the letter t and the vowel —unless that vowel is a capital letter (for example, an tUachtarán the President).
Cén is Cé+an, so you get cén t-am and cén t-ainm because am and ainm are masculine nouns, and you get cén áit and cén ois because áit and aois are feminine nouns.
It would be cén uair rather than cén huair. In Munster, it would be cá huair
Cén uair? does mean "when?" but I'm not sure that it's used for asking what time it is now - (possibly because uair is a bit imprecise for "clock time", though that might just be béarlachas or just an overly modern attitude to time).