To make the time and date appear, first you need to access Config > Date to set the current time/date. To make it more accurate, use the NTP synchronization and make sure the camera is connected to the Internet. This will update the date/time automatically. After this operation, the date and time stamp will be embedded in your videos.
Additionally, you can change the time and date for every channel where the cameras are connected. Use the option from the bottom-left area of the Date section.