One problem with the 12 hour clock is that if AM or PM is omitted or unreadable, you are could be very early or very late for your appointment.
The 24 hour clock eliminates any ambiguity and does so without making the number of characters used any longer. In fact it makes it shorter (01:00 is shorter than 1:00 AM).
In Blanchardstown Centre they want to really, really sure that there is no confusion as to when the on-site creche closes. It doesn’t close at 5:00 PM. It doesn’t close at 17:00. No, it closes at 17:00 PM!
At least the addition of “PM” is shorter than adding “in the morning“