When do you blow out the shabbat candles?

It is forbidden to light or extinguish a flame during Shabbat. For this reason, you would not blow out the Shabbat candles. You would let them burn our themselves. There are Shabbat candles specially made for this that will burn for about 3-4 hours, a perfect amount of time to stay lit during dinner, but allow you to go to bed without worrying about leaving a lit candle.