How do you remember which way the clocks go from one country to another? How about the USA and UK and Europe. I remember that when Kennedy was assassinated, it was afternoon in the USA, but we turned on the TV in London, England, in the evening.
I remember that when we lived in Washington DC the latest we could phone my parents in London, England was when my son came home from school, and if my husband came home from work early. Depending on the time of year, for British summer time. I ended up writing a note above the phone of the hours in the USA when I could phone the UK.
Night Time Or Day Time
My most embarrassing moment was phoning the USA from the UK. I had received a Christmas card from somebody in the USA after my uncle died. No address on it. They had not bothered because he knew their address. I remember when I was a teenager you always wrote the sender's address on the back of a letter so that if the letter was misdirected the post office did not open the letter to try to find the sender's address. Nowadyas with security concerns, people are less keen on putting their address on the back of the envelope. But an address inside could be helpful.
Anyway, months later, I was reading through all the entries in my late uncle's address book to try to distinguish the business addresses form the friends. Even the businesses had to be told he had died, so that they did not waste time and effort sending him reminders and offers. I came across an American address. That was it! The sender of the Christmas card. Maybe not, but I had the number so at least I could try.
I was so pleased to have solved the mystery that I grabbed the phone immediately to call whilst I had the number in front of me.
The phone rang for ages. I was disappointed, and had almost given up, when somebody answered. She sounded sleepy. I wondered if she was having an afternoon nap.
I told the puzzled woman at the other end, "You don't know me but I'm the niece of my late uncle Ronnie and I am sorry to have to tell you that he - has died."
After a silence, she said, "Ronnie who?"
"Ronnie from England."
She replied, "I am sorry to hear that your uncle has died. But I cannot recollect anybody in England called Ronnie."
"Ah," I said, Maybe you knew him by his professional name, Arthur."
"Oh, Arthur!" she replied. "Oh, no! I am so sorry. I am sorry if I sound a bit confused, but over here in California it is 4 am. And I was asleep."
I replied, " Oh my Go -sh. I hadn't realised. Shall I ring back tomorrow?"
"No," she said. "Let's talk. I am wide awake now."
Even if I had thought about the time I used to make calls to and from Washington DC I would have got the time wrong. America is thought of as a country, but it is actually a continent. Not only in terms of size, regarding population and politics. In terms of geography, the setting and rising of the sun, the time zones.

California, USA.
The USA has more than one time zone. People in New York might already be at work. People in California might still be asleep.
The moral is, check the time zone overseas, the country and the area, before you call.
24 Hour Clocks
I'll see you at nine could be nine in the morning or nine in the evening. To the speaker it seems obvious. To the listener it is no always clear. Many tickets use a 24 hour clock to avoid conclusion. This can cause more confusion if you just look at the last number and think that 14.00 if four o clock when it is 2 pm.
To be doubly safe, write down both systems, 14.00 hours (2 p.m.)
May you always arrive on time, on the right day!
Useful Websites For Travellers & Phone Callers
https://www.timeanddate.com/worldclock/usa
https://en.wikipedia.org/wiki/Date_and_time_representation_by_country