The new date for the Ethereum Constantinople Hard Fork has been announced by the core developers of Ethereum. The Hard Fork will no happen upon reaching block 7.280.000 which should happen on the 27th February 2019.
The initial Hard Fork date had been pushed back after a serious bug had been discovered in the new Ethereum code that could have allowed malicious actors to steal funds from Ethereum users. The EIP-1283 where the „Reentrancy Bug“ had been found after an audit was subsequently scrapped. There have also been rumors that the developers are looking for a new name for the hard fork.
It is no again important for miners to update to the new code in time, to continue mining. Normal Ethereum users will not have to do anything, as there are no major changes planned for them.