If you are getting a refund you don't need to get an extension. If you have a tax due the payment was still due by April 15 even if you had an extension. The extension is only to file the return. You can efile until Oct 15. After that you can print and mail your return. You have 3 years to file for a refund.
Do you need to get on payment plan? You can file and say you will mail a check, then apply for a payment plan.