Firstly head over to the 000webhost members area and login!
Once logged in hit manage on your site
Once this loads
Hit Settings top right and choose General
Browse down just over half way and you’ll see sleep settings
Set your website to sleep for an hour (from the 1st November 2017) i.e. midnight until 1am
I would pick a time that you expect nobody to be online i.e. in the middle of night
If you feel you need your website round the clock you might be better moving onto Hostinger where there are no limits at all and much more features on their premium but affordable servers.