>>822
大体1秒、2秒で良いなら

private async void Form1_Load( object sender, EventArgs e )
{
var odd = false;
while ( true )
{
await Task.Delay( TimeSpan.FromSeconds( 1.0 ) );
this.textBox1.Text += "1";
if ( odd )
{
this.textBox2.Text += "2";
}
odd = !odd;
}
}