Just coordinate via asynchronous communication to schedule a time. It’s not 1935.

You: “hey uncle text me when it would be a good time to have a call”

6 hours later

Uncle: “hey i just got up, lets have a call at 4:50”

You: “thats a bid late for me, im in bed by 4:00, what about 3:30?”

Uncle: “sure sounds great”

No one needed to know anything about when people wake up, where on earth they live, etc.