Currently network weight is almost 485,000... phenomenal network support as we move to less than 5,000 blocks until the next DPOS reward increase to .8 GRWI per block.
How long do I have to keep coins in wallet to stake? I see the message "not staking coz your coins are not mature".
The period for your coins to mature is 8 hours. After they have matured, you have the chance of staking blocks. The higher your wallet weight in comparison to the total network weight, the higher your chance of getting a stake reward.