Not knowing what stat you are from, it is hard to say.
My helper told me over the phone that if you know you will be oweing taxes you should pay the amount you are expected to owe before the April 15th date and then file your taxes after your federal has been filed. Just because you are out of the country does not exempt you from having to pay taxes or allow you to pay them later. If you are owed taxes and you did not pay them you will be charged a penalty late charge and interest. However, if you know you do not owe any taxes, you can file later without any notification.
As I said before, state rules vary so it would be best to give your state tax office a call.