If you are using the DATE instruction in the PLC to set it via the HMI, you must also set the Day of Week value correctly (LOW BYTE in the LOW WORD, BCD). You cannot set the V7774/V7773/V7772/V7771 values directly, those are READONLY and set by the PLC firmware from the time-of-day chip in the PLC hardware. To set the time-of-day chip, you must use the DATE (and TIME) instructions.