Unable to reach you

Here’s the scenario...

You go to call a friend or family member and they don’t answer. How long do you give them to call back before you worry?

My MIL stopped by unexpectedly because we didn’t answer the phone at 5:30 and 6:00. She was here at 6:30. Also important to note my partner answered her first call at 4:30 and said he would call her later as he was on the bus and it was too loud to talk. She thinks we’re crazy for saying that she needs to give us 24 hours to call back before she sends a search party. I think it’s weird that she expects us to answer every single call.

So what’s the norm? How do you deal with unanswered calls?