What's the simplest way to sync clocks over the network?

Basically, I need everyone to have a timer that is synchronized to the server's timer down to the millisecond.

After the server sees that all the clients are ready, it will tell all the clients to perform an action at a certain comming time.

This action would basically be the start of the race and would have to happen all exactly the same time as everyone else. It's only fair to let everyone start the race at the same time.

I initially thought Network.time would do the trick, but I guess it's actually how many seconds your machine has been turned on for- Right?

I'm confused on what I need to do to make this happen... Any help would be very appreciated.