I received my DTV before my ED visa expired, had no issues. You just have to tell your school that you are canceling your ED visa and then it'll take them a week to give you a letter stating that your studies have concluded and then you take that letter to immigration to cancel the extension of your Ed Visa if you were still on one. You have to bring the letter, your passport and also photocopies of your passport pages. It doesn't interfere with your DTV in my experience.