In the Redmi 4 smart phone, please go to the settings icon, then the device or system apps icon. This will show the list along with the camera.
Once you click on the camera, you will see a list that you can scroll up and down, it will include 'Add time stamp on photos' activate it or push it to on mode and save the settings.
After this is done, click a picture and when you view it, you should see the date and time stamp in the right lower corner.
If the phone does not have this option, then you can use any of these apps
Photo Stamper free version
Many of the photo editing apps like camera360, Photoscape etc allow you to add the date and time stamp too.
There are some who prefer not to add the date and time stamp as it looks odd.
One can retrieve the image date and time details by viewing the Exif specifications. All images take will have this data - exchangeable image file data. This will usually have shutter speed, aperture, file size, date and time.