The Daily Rewards feature gives you a reward for each day you login for the current calendar month. The final reward is given on the 24th day, meaning if you miss a few days you can still receive the final reward.
At the top right is displayed the number of days until reset, which is the 1st calendar day of each month.
If you started your game and there is less than 24 days until the beginning of next month, unfortunately you will not be able to earn the final reward for the current month.
NOTE: Once you reach the 24th day reward, no matter the calendar day you reached it on, you will need to wait for the 1st day of the following calendar month to start the next batch of Daily Rewards.