UNetWeaver rror, failure generating network code, and a lot of confusion about the networking process comprehension issues

So, I've been exploring Networking through Unity, it's not an especially complicated process that I am trying to accomplish, in my opinion. I am simply trying to utilize application users to update and share Timer information between one another. Eventually, I will likely remove the Instantiation process from this area, as I determine duplicate timers and the likes, but for now, I am working on simply creating new timers based upon the input received from fellow users creating timers on their end, and outputing one's own created timers to fellow users in response. I thought I was getting somewhere, a real touch and go process, but ultimately despite my code being 'apparently' error free, syntax wise at least, it seems like there is a gap in my understanding which has caused me to run into an error I don't understand.

 UNetWeaver error: Script NetworkManager uses [SyncVar] ItemName but is not a NetworkBehaviour.
 UnityEngine.Debug:LogError(Object)
 Unity.UNetWeaver.Log:Error(String) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/Program.cs:20)
 Unity.UNetWeaver.MonoBehaviourProcessor:ProcessSyncVars() (at C:/buildslave/unity/build/Extensions/Networking/Weaver/MonoBehaviourProcessor.cs:31)
 Unity.UNetWeaver.MonoBehaviourProcessor:Process() (at C:/buildslave/unity/build/Extensions/Networking/Weaver/MonoBehaviourProcessor.cs:18)
 Unity.UNetWeaver.Weaver:ProcessMonoBehaviourType(TypeDefinition) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/UNetWeaver.cs:1126)
 Unity.UNetWeaver.Weaver:CheckMonoBehaviour(TypeDefinition) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/UNetWeaver.cs:1639)
 Unity.UNetWeaver.Weaver:CheckNetworkBehaviour(TypeDefinition) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/UNetWeaver.cs:1650)
 Unity.UNetWeaver.Weaver:Weave(String, IEnumerable`1, IAssemblyResolver, String, String, String) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/UNetWeaver.cs:1791)
 Unity.UNetWeaver.Weaver:WeaveAssemblies(IEnumerable`1, IEnumerable`1, IAssemblyResolver, String, String, String) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/UNetWeaver.cs:1888)
 Unity.UNetWeaver.Program:Process(String, String, String, String[], String[], IAssemblyResolver, Action`1, Action`1) (at C:/buildslave/unity/build/Extensions/Networking/Weaver/Program.cs:34)
 UnityEditor.Scripting.ScriptCompilation.EditorCompilationInterface:TickCompilationPipeline(EditorScriptCompilationOptions, BuildTargetGroup, BuildTarget)

 Failure generating network code.
 UnityEditor.Scripting.ScriptCompilation.EditorCompilationInterface:TickCompilationPipeline(EditorScriptCompilationOptions, BuildTargetGroup, BuildTarget)

Here is the code that I am utilizing, so perhaps someone can explain where the error is at, or what is missing that I don't yet understand well enough to find.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.Networking;
 
 public class NetworkManager : MonoBehaviour {
 
     public bool isAtStartup = true;
     NetworkClient myClient;
     NetworkTimer nt;
 
     //collects Prefab and Container for NetworkTimer class
     public GameObject Timer;
     public GameObject Content;
 
 
     // Update is called once per frame
     void Update()
     {
         //The Server is a Client
         //The Client is a Server
         //The Cake is a Lie
         if (isAtStartup)
         {
             nt.SetGameObjects(Timer, Content);
             SetupServer();
             SetupLocalClient();
         }
         else
         {
             NetworkServer.Listen(4444);
             myClient.RegisterHandler(MsgType.UpdateVars, nt.UpdateTimer);
         }
     }
 
     // Create a server and listen on a port
     public void SetupServer()
     {
         NetworkServer.Listen(4444);
         isAtStartup = false;
     }
 
     // Create a local client and connect to the local server
     public void SetupLocalClient()
     {
         myClient = ClientScene.ConnectLocalServer();
         myClient.RegisterHandler(MsgType.Connect, OnConnected);
         isAtStartup = false;
     }
     // client function
     public void OnConnected(NetworkMessage netMsg)
     {
         Debug.Log("Connected to server");
     }
 }
 
 //Requires NetworkBehaviour for SyncVar
 class NetworkTimer : NetworkBehaviour
 {
     //Can't utilize MonoBehaviour as a result
     private GameObject Timer;
     private GameObject Content;
 
     //Required Variables to Sync, error?
     [SyncVar]
     public string ItemName;
     [SyncVar]
     public float CookTime;
     [SyncVar]
     public float HoldTime;
 
     //Functionally importing GameObject References
     public void SetGameObjects(GameObject timer, GameObject content)
     {
         Timer = timer;
         Content = content;
     }
 
     //Receives Network Message to UpdateVars with the contained variables in the message?
     //How?  Or am I lacking a crucial detail here?
     public void UpdateTimer(NetworkMessage netMsg = null)
     {
         GameObject timer = Instantiate(Timer, Content.transform);
         timer.GetComponentInChildren<TimerHandler>().Set(CookTime, HoldTime, ItemName);
     }
 }
 
 //Almost useless, since this is it's only function, but seems significant still. 
 public class MessageTypes
 {
     public static short UpdateVars;
 }
 
 //Msg contents, wonder if I need to refer back to here,
 //and maybe include a function to apply these variables when receiving this message?
 public class TimerMessage : MessageBase
 {
     public string name;
     public float hold;
     public float cook;
 }
 
 //Code Snippets and Tutorials don't make for easily readable code...
 //So, here is where I have been sending messages, based on what the user is creating
 // while also trying to handle the data route from this place as well, so that regardless of whether
 // it is sent or received, it takes the same route to creation.
 class GameServer
 {
     NetworkTimer nt;
     public void SendTimer(string productName, float holdTime, float cookTime)
     {
         TimerMessage msg = new TimerMessage
         {
             name = productName,
             hold = holdTime,
             cook = cookTime
         };
         NetworkServer.SendToAll(MessageTypes.UpdateVars, msg);
         nt.ItemName = productName;
         nt.HoldTime = holdTime;
         nt.CookTime = cookTime;
         nt.UpdateTimer();
     }
 }