Date Time Difference log

[mandukes]

Hi how to get the date time difference? Looking for a date time stamp which logs the date and time and returns the difference of any previous date and time.

For example : Today 18/11/2017 9:52:42:21 AM - 12/11/2017 5:40:42:10 PM

Just want to detect if a user tempered with system's date and time and edited a worksheet.

Thanks