Use iMovie.
Drop a clip on a Project and then open the Title Bar and Drag and Drop the Date/Time Tittle over the clip.
Beware of some problems displaying the correct time due to your Mac's timezone options. I'm currently in -5 GMT and with the 9.0.6 version the Date/Time Tittle will substract 5 hours from the original time. Older versions didn't have that problem.
Also beware of a mobile phone issues. Iphone / Android will write the date and time of its video files when the file ends so you need to substract the lenght of the clip from the time shown on the file.
Hope this helps