It cannot work for variables received from connected PLC; by definition!
I can only repeat again what I had posted in this thread in July: the value, status bits (e.g. quality) and time stamps by process variables are always like the PLC sends to zenon in telegrams, not simply like the user wish to have. When in zenon, the user sets value to the variable then the driver sends this write request to the PLC. As next the driver receives the (hopefully updated) value from PLC (eventually with some external time stamp given by PLC) and this is what you see as the result in zenon. If PLC is delivering the variable value without external time stamp, then the time stamp of the value is from the moment of the data reception, not some faked one.

zenon - for process variables communicated from devices - always displays the data received from devices, and there is no way to fake it. If you like to force device to take over your artificial time stamp - change in the device the PLC programming accordingly.