When exactly is the AWT thread started?

Anytime the java.awt.Toolkit instance is (directly or indirectly) created. The direct way to create it is by calling-

Toolkit.getDefaultToolkit();

Indrect way is by creating any AWT object.

Here is a sample program to play with -

import java.awt.*;
public class X 
{
	static Frame f;
	
	public static void main(String[] args)
	{
		//Toolkit.getDefaultToolkit();
		f = new Frame();
		System.out.println("...");
	}
}