lightning network is not exactly something that is implemented one day. it is like a protocol which is already there and now there are applications being built based on it.

it is like asking when will bitcoin be implemented! bitcoin protocol is already there, and many programs are built to use it such as bitcoin core, electrum,....

currently the L network is up and running with 101 nodes and 229 channels,
https://bitcointalk.org/index.php?topic=2796578.msg28589053#msg28589053
these "programs" that i talked about are still in testing phase but you can start using them for testing and contribute to their development.
Lightning Network Daemon https://github.com/lightningnetwork/lnd
a Lightning Network implementation in C https://github.com/ElementsProject/lightning
Lightning Network desktop application https://github.com/LN-Zap/zap-desktop
and a lot more.