When it comes down to earning DEC, it works with capture rate % which is very similar to how voting power works on Steemit. Each game you play drains some of the % which lowers the earnings and it regenerates over time. Each day you get a daily quest to complete which gives reward cards when completed within 24 hours. They can be completed at any time during a 24 hour window. (they usually take me 20 minutes to complete in Gold/Diamond League) . There are also season reward cards based on your ranking every 15 days are tournaments also start (I rarely join them) at specific times each day.

Good Luck