"Lunch starts at twelve."

Translation: Prânzul începe la doisprezece.

[Lachlan_Hunt]

Why is douăsprezece not accepted?

[Ces.10]

Because you use the masculine word when you speak about a point in time. 2 o'clock = la ora doi, 12 o'clock = la ora doisprezece. But oră IS a feminine word so when you are counting hours its different: 2 hours = două ore, 12 hours = douăsprezece ore.

[lpaulger]

"pranzul incepe la ora douasprezece" isn't incorrect is it?

[KevinSmith777042]

Surely ora is either male or female - or how would one choose when to use which?

[Ces.10]

It's feminine, but that only matters when you are couting hours. E.g. 2 hours = două ore, but 2pm = la ora doi.