How can I know the true time and date stamp on my pictures in my phone

If they were taken by you, on that actual phone, then they should be time stamped with the date and time the phone has. You just need to open any given image and then look at the info for the image.

 
Why would you want to change real date and time on a photograph I guess if your playing f#!; f#!; games then you would sincerely antmac