As a point of clarification, the newest member benefit, which was initially branded as "Daily Assignment Double Rewards," works just a bit differently than we might have led you to believe. If we run this promotion again in the future, we'll be calling it something along the lines of "Member Daily Rewards Bonus."
While Gold, Arena Tickets, and Crowns are in fact doubled, instead of doubling the rewards you usually get for opening chests on Days 5, 10, and 15, during the event there's a special loot roll that normally isn't available for Daily Quests while the Member Daily Rewards Bonus is active.
If you have a quest on Day 12, nothing changes on this day from what you usually receive.
Sorry for any confusion and we hope you enjoy this new member benefit. We are listening to your feedback and appreciate your support.