Learn Russian: Мы приехали часа за два до вылета. - We arrived about two hours before the flight departure.

In Russian, swapping the normal order of a number and a noun expresses approximation. The standard order за два часа means exactly "two hours before". By putting the noun first as часа за два, it changes the meaning to "about two hours before".

Wait, the lesson says to use за + accusative for the time. Why is часа in the genitive case?

The entire phrase два часа is the object of за, and it is technically in the accusative case here. For inanimate nouns, the accusative form of the number два is just два. As a rule, the number два forces the following noun into the genitive singular, which gives us часа. Even though the word order is flipped for approximation, this internal grammar rule for numbers remains exactly the same!

Why do we use до вылета here instead of перед вылетом, if both can mean "before the flight"?

When you state a specific amount of time before an event (like "two hours before"), you must use the за ... до ... formula. You would use перед вылетом (which uses the instrumental case) if you were simply saying "before the flight" without measuring the time elapsed.

Is вылета the genitive form because of the preposition до?