Learn Turkish: Bir saat altmış dakika. - One hour is sixty minutes.

Yes! Saat is a very useful word. It can mean "hour" (as in this sentence), "clock", or "watch". When asking for the time, you also use it: Saat kaç? (What time is it?).

Why is it just dakika and not plural (dakikalar) after the number sixty?

In Turkish, nouns always stay in their singular form when they come after a number. So you say altmış dakika (sixty minute), never altmış dakikalar.

Where is the word for "is" in this sentence?

There isn't one! In Turkish, basic statements don't need a verb for "to be" in the present tense. You just put the two parts together: Bir saat (One hour) + altmış dakika (sixty minutes).

I sometimes hear people say "atmış" instead of altmış. Are they the same?

Yes, they are exactly the same. Altmış is the correct spelling for "sixty", but in spoken, everyday Turkish, people often drop the "l" sound and pronounce it "atmış".