Tell me, how much maturity of the coins on staking, something is not clear, shows then 5 days before the award, then back 6.7 days?
Maturity is 24 hours. That is when the transactional block of coins starts to gain weight, not when to expect a reward.
When to expect the reward has many, many variables, such as the number of coins and external variables such as the number of other's coins being actively staked at that point in time.
Estimations of when to expect the next reward are only estimations formed at that point in time and if all variables remained unchanged. But they undoubtedly will and do change. This is why estimations will not be consistent over time.
I hope I have answered completely. Thank you for staking your EverGreenCoin!