In my chat app, if a person sends messages from EST and the other person responds in CST, the order of messages displayed are off because the EST user's timestamp is 4:00pm when the CST users's timestamp is 3:00pm. (assuming they replied around the same time). Because the order of messages are sorted by the timestamp, the 3:00pm (CST reply) shows above the original message sent at 4:00pm EST.
I'm currently using the 'Current Time' in the Global properties to assign the timestamp when the user sends.
What's weird is that I've only recently noticed this happening and I've had this app live for a couple of months now.