Going back to the original post, it does NOT take 3 hours to screen international passengers. In fact at just about every US airport I have used, domestic and international depart from a mixed use set of gates (arrivals are different due to the need for customs etc). Nor have there been any changes to Minimum Connecting Times for domestic to International flights. I don't know where this comes from.
Reminds me of a travel agent in the UK who told me that a flight at 0700 from London Cityto Paris required an absolute minimum check in of 2 hours "because it is international". I pointed out that the London City terminal building was not even unlocked until 0515 in the morning.
Regarding the 24-hour clock (known in the US as "Military Time"), I believe that all international carriers from the US use this and have done for many years. In fact I have just had a quick look at all the Pan Am(of all carriers) flight timetables in my historic collection from the 1950s-60s, and they all have times in the 24 hour clock as well. So I don't know where that one comes from either.