Daily Bonus is a reward you can claim every day. You may claim boosters.
The daily bonus was started in June 2014. It has one or two gold bars in the bonus. There was boosters, 2 extra moves, and treasure of two or three boosters. Then Atomic Orb was added as a booster in 2015. Treasure Mine was started in 2015, so they complete a level to get boosters. On mobile, it was started bonus in 2015, and did the same thing on web. Every 23 days, it was renewed. In 2016, a brand new bonus appeared on web. It has five days. The atomic orb is on the fifth day, so they want to start over when you miss a day. On mobile, it remained 23 days, without gold bars. There was more boosters. Treasure mine was removed on Disco Circo. In 2016, the fourth day is a 5 extra moves booster, was changed to dynamite and added a atomic orb on the fifth day.
In 2018, the old daily bonus calendar was reverted back into a 23 day daily bonus calendar because an update of Diamond Digger Saga web version was on mobile version. On every 23 days the daily bonus was renewed.