"* I want to call my friend in Germany. It's the same time here as there. It rises at 13:00 here, but she's a quarter of the way way around the world. I have to

"* I want to call my friend in Germany. It's the same time here as there. It rises at 13:00 here, but she's a quarter of the way way around the world. I have to look up their typical waking hours. She's an early bird, so is she on the early side of that, likely. What time does the sun rise there? How much does that change over the seasons?" In both cases you need to do some maths. You know early birds wake up at 11 where you live. If you know she's 8h ahead, just add 8. So, 19 is when you should call. For calling people nothing really change. Adapting when moving somewhere else is the tricky bit. If I move to another city or country I just adjust my clock and automatically know when things will be open, working hours, etc. Otherwise, whenever you move you have to keep mentally reminding yourself that the work day starts at 12 here, not 7 like I'm used to and so on.