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Szabolcs,
When relating to time, "σε" means simply "at", when used with hours (other time indications use the accusative case). "στις επτά": at 7 o'clock. "Από", on the other hand, means "since", and is the opposite of "ως": until.
Now, it may seem weird to say "I have to wake up since 7 o'clock". It's probably even ungrammatical in English. In Greek on the other hand, it's a normal construction. I'm not sure I can explain it right, but it's as if they are taking the future point of view of arriving at school on time. The sentence could probably be more accurately translated as: "in order for me to be at school on time, I'll have to have been up since 7 o'clock", although it's a bit awkward in English.
Another way to look at it is that using "στις επτά" would make the sentence a simple statement of fact: "I have to wake up at 7". Using "από τις επτά" connects it back to the reason why the person has to wake up so early. Less than a statement of fact, it becomes the result of a condition.
I've noticed that Greek sometimes uses "ως" in a similar way, but this time connecting to events happening before the timed event. It can be a bit difficult to understand at first, but you get used to it. |