Every day has a single challenge of thirty words, and everyone gets the same words on the same day. The difficulty rotates through the week, so the challenge is not the same shape every time and a beginner meets an easy one within a couple of days.
Finishing it extends your streak, and the bonus grows with the streak — so a run of days is worth considerably more than the same number of sessions scattered across a month. Accuracy raises the bonus too. You can replay the day as often as you like for practice; the bonus is only paid once.
Also try: a drill for your weak keys · a race