Firstly make sure all this has finished before the timer event fires again and restarts your function.
TextBox.Text.Length does not return a string so
If TextBox1.Text.Length = "26"
is the wrong thing to do.
When you say "not working" do you mean it won't compile? If I was writing those If-statements they would look something like
If TextBox1.Text.Length = 26 Or TextBox1.Text.Length = 27 Or TextBox1.Text.Length = 28 Or TextBox1.Text.Length = 29 Or TextBox1.Text.Length = 30 Or TextBox1.Text.Length = 31 Or TextBox1.Text.Length = 32 Or TextBox1.Text.Length = 33 Or TextBox1.Text.Length = 34 Or TextBox1.Text.Length = 35 Then
Well actually, it wouldn't, it would look more like
If TextBox1.Text.Length >= 26 and TextBox1.Text.Length <= 35
One final point - don't tag your question as C# if it's VB.NET!