Bearing in mind that you live in a flat, you will make yourselves very unpopular with your neighbours if you run your washing machine late at night.
That all depend on how old and noisy your appliances are!
We have been running our washing machine, dishwasher and tumble drier overnight for years and they have never woken us up. The secret is to set them to come on so they finish just as you are getting up.
Making a big assumption here, but you live in a house, you sleep upstairs and the machine is downstairs?
In the case of a flat (as it was in my case) the machine is above you, with only a few inches of concrete between it and your flat. I can tell you for a fact that when that machine is on at 3am you will definitely hear it - LOUD!
People who live in flats and think its OK to run washing machines at 3am (whilst also doing the hoovering!! - but thats another story) should be taken out and shot