Agreed. If they need the subpoena in a hurry, they can call the judge at night and get him out of bed and make their case.
This is like with the wiretaps. Any time, day or night, a judge is available to sign-off on anything as long as it is legitimate. When powers like this are granted, it would seem that the real reason is to execute subpoenas and other warrents that the government doesn't believe they would be able to convince a judge was valid.