Tech support forwarded a question from an individual hoping to add timestamps to messages. I came up with an interesting technique which amuses me, in part because thinking of it made me feel clever, and in part because it relies on one of the most hated options in the system. Paste the following cell into a private stylesheet for a given notebook, then start creating messages...
Cell[StyleData["Message"], CellFrameLabels->{{Cell[BoxData[FormBox[DynamicBox[ToBoxes[DateString[First[Flatten[CurrentValue[ParentCell[EvaluationCell[]], CellChangeTimes]]], TimeZone -> 2 $TimeZone], StandardForm…