I am trying to make a simple GUI that when opened shows the current world time.

I want the time to be updated per tick, but I cant figure out where the "update" function is called.

Any clues?

GuiScreen#updateScreen.

Hi

You could also do this in an event, if you would like. This can be done using ClientTickEvent or RenderTickEvent (each ran on the client side, I believe), called on the FMLCommonHandler BUS. If the update method is easier, by all means use it.

@SubsribeEvent
public void clientTickEvent(ClientTickEvent par1ClientTickEvent)
{
    //Make sure to null check the world here
}

@SubsribeEvent
public void renderTickEvent(RenderTickEvent par1RenderTickEvent)
{
    //Make sure to null check the world here
}

//Register the classes that contain these events in your pre-Init
@Mod.EventHandler
public void preInitializationEvent(FMLPreInitializationEvent par1FMLPreInitializationEvent)
{
    FMLCommonHandler.instance().bus().register(new YourClassWithTheEvents());
}

I also want to add on the fact of this:

Would you like to recieve information on the server / exchange information between the client and the server? If so, you need to send packets. I know that you just want to display something on the screen every tick, bu getting this type of info is useful. Here is an extremely helpful tutorial on packets for the SNW (SimpleNetworkWrapper) by coolAlias:

https://github.com/coolAlias/Tutorial-Demo