You'll earn diamonds once you've played 5 min a day for 7 days in a row.
If you continue playing your streak past 7 days, you'll start earning diamonds every day (for playing 5 min) instead of a weekly reward.
You'll continue to earn these units every day until you’ve stopped playing for a day.
You can find the timer on the bonus tab:
You need to play before the timer runs out to continue your daily streak
Once you've stopped playing for a day, your streak will reset, and you'll have to complete your weekly challenge again (Play 7 days in a row) to start receiving your daily rewards.