CustomNetworkManager.cs

using UnityEngine;
using System.Collections;
using UnityEngine.Networking;

public class CustomNetworkManager : NetworkManager
{
	#region Server side

	public override void OnStartServer ()
	{
		base.OnStartServer();
		// we're the Server, dont need to sync with anyone :)
		_isSyncTimeWithServer = true;
		syncServerTime = Network.time;
	}

	/// <summary>
	/// On server, be called when a client connected to Server
	/// </summary>
	public override void OnServerConnect (NetworkConnection conn)
	{
		base.OnServerConnect(conn);
		Debug.Log("---- Server send syncTime to client : " + conn.connectionId);

		var syncTimeMessage = new SyncTimeMessage();
		syncTimeMessage.timeStamp = Network.time;
		NetworkServer.SendToClient(conn.connectionId, CustomMsgType.SyncTime, syncTimeMessage);
	}

	#endregion



	#region Client side

	public override void OnStartClient (NetworkClient client)
	{
		base.OnStartClient(client);
		client.RegisterHandler(CustomMsgType.SyncTime, OnReceiveSyncTime);
	}


	void OnReceiveSyncTime(NetworkMessage msg)
	{
		var castMsg = msg.ReadMessage<SyncTimeMessage>();
		_isSyncTimeWithServer = true;
		syncServerTime = castMsg.timeStamp;
		Debug.Log("--------Client receive : " + syncServerTime);
	}

	#endregion


	#region Update sync time

	/// <summary>
	/// Use this, instead of Network.time . Sure this var will be
	/// sync on both Server and all connected clients
	/// </summary>
	public static double syncServerTime;

	/// Do we receive the syncTime from Server ?
	bool _isSyncTimeWithServer = false;

	void Update()
	{
		if (_isSyncTimeWithServer)
		{
			syncServerTime += Time.deltaTime;
			// This Log just to show the syncTime to console for testing purpose
			// remove it in your project
			Debug.Log("SyncTime : " + syncServerTime);
		}
	}

	#endregion
}

#region Custom classes

public class CustomMsgType
{
	public const short SyncTime = MsgType.Highest + 1;
}


public class SyncTimeMessage : MessageBase
{
	public double timeStamp;
}

#endregion