You'll earn diamonds once you've played 5 min/day for 7 consecutive days.
If you continue playing after completing your weekly streak, you'll start earning diamonds every day (for playing 5 min) instead of a weekly reward.
You'll continue to earn units every day until you lose your 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.