Learn Italian: Questo è un momento importante.

While many Italian adjectives change their ending to match masculine (-o) or feminine (-a) nouns, there is a second group of adjectives that always end in -e in the singular. Importante is one of these, so it stays exactly the same whether describing a masculine or feminine word.

Why is it un momento and not uno momento?

We use the indefinite article un before most masculine singular words starting with a consonant. Uno is a special article saved only for masculine words starting with 'z', or an 's' followed by another consonant (like uno studente).

Since this lesson is about telling time, can I use momento to ask about clock time?

No, momento simply translates to a 'moment' or 'instant'. To ask about clock time, you must use the word for hour, which is ora (for example, Che ore sono? meaning 'What time is it?').