How can I find the response time (latency) of a client in NodeJS with sockets (socket.io)?

I'm trying to create a multiplayer game with NodeJS and I want to synchronize the action between clients.

What would be the best way to find the latency (the time that a request take to come back to the client) between the client and the server?

My first idea was that the client #1 could send a timestamp with is request, so when client #2 will receive the action of the client #1 he will adjust is action speed to remove the delay of the request. But the problem is that maybe the system date time of the two clients are not identical so it is not possible two know the reel delay on the request of client #1.

The other solution was to use the timestamp of the server, but now how can I know the latency of a client?