Because you have clients across the country, please either show times in the user's time zone or list the time zone used in the time-stamp.

For example, I have a message from a client that was supposedly written at 4:30-ish this afternoon. Unfortunately, I know for a fact that the message must have come in around 7 pm. Timing is important when it comes to connection issues with the teletherapy program, fees for late cancellations, etc.