I work with a team in a time zone about 12 hours off of mine, so we are almost never online at the same time. I sent one guy on that team a message at 3AM his time, and he got all annoyed that I was expecting him to work at 3AM, and I was like no dude, just respond when you start working. So now whenever I sent messages to that guy, I always prefix some text about how this isn't urgent and to ignore it until his work hours start.