According to the immigration website, you need 15 days visa validity to convert a TR to a non-b visa. However, this doesn't make much sense to me as last time I did it the non-b was stamped on the same day as I made the application, so why the need for 15 days? And I'm informed that as long as you're not on overstay, your application will be accepted. So if I turned up to immigration with all my documents in order with 3 days left on my visa, would they accept it or would I need to get the TR visa extended by 30 days and then make the application? That would seem completely nonsensical if the non-b was going to be granted on the same day anyway.