12 hour fast

I don't understand how to work the 12 hour fasting out. I mean I know you fast for the 12 hours but I wanted to eat late at night like at 10pm or so. Otherwise I'm hungry all night trying to sleep. But I also need the 12 hours to occur while I'm trying to sleep. But 10 at night means 10 in the morning then nothing all day.
That means I'm fasting all day? What happened to the fasting occurring while I'm trying to sleep?
I can't figure it out.