the wireless stick when connected to a PC is a simple MSC device. It is not running any real time clock and has no setting to change any date and time. Is the clock on the PC correct? Do you see similar issues when transferring files to other USB drives?
Files transfered to other USB sticks retained their modified time.
Files transfered to the Sandisk Wireless Connect via its wireless connection have their modified time changed to current time of my PC plus 8 hours (future time).
Files transfered to the same stick via USB connection retained their modified time.
wireless transfer is a bit different type of transfer than direct connect. Date modified will be changed but the date created should stay the same. If you need the file to retain the same data modified date when using with a computer I would suggest using the USB connection.