Discover Weekly is once a week: on Mondays. You're thinking of Daily Mixes, of which there are 6 that update throughout the week, one playlist per day.

To go along with Discover Weekly there's also a Release Radar playlist that updates every Friday with that week's new releases from your artists.

Spotify is so deeply engrained into my weekly schedule that I really look forward to the Discover Weekly and Release Radar playlists bookending my work weeks.