There are no standards established for the meaning of 12 a.m. and 12 p.m. It is often said that 12 a.m. Monday is midnight on Monday morning and 12 p.m. is mid-day. This puts all the times beginning with 12 and ending with a.m. in the same one-hour block, similarly with those ending with p.m. It can also be argued that by the time you have seen a clock showing 12:00 at mid-day it is already post meridiem, and similarly at midnight it is already ante meridiem. Times in the first hour of the day are sometimes given as, for example, 00:47 a.m., with 00:00 a.m. corresponding to midnight, but with a time twelve hours later given as 12:47 p.m.

Q: Can prospective travelers apply for an ESTA™ without specific travel plans if they want to be able to travel to the United States later on short notice?
A: Yes. VWP travelers are not required to have specific plans to travel to the United States before they apply for an ESTA™. VWP travelers are not required to complete the travel itinerary and destination details before submitting an ESTA™ application. If a traveler’s destination address in the United States is unknown when he or she completes the ESTA™ application, the traveler may enter the name of the hotel or approximate location he or she intends to visit. Travelers may update this information when their plans are finalized, but they will not be required to update their destination addresses or itineraries should they change after their ESTA™ has been approved. DHS recommends that ESTA™ applications be submitted as early as possible, as soon as, or even before travel is planned. ESTA™ will accept applications from last minute and emergency travelers – those VWP travelers that arrive at the airport without an approved ESTA™.