DirDate is a command line tool that can easily be automated to change files' last modification date, creation date or last access date. It can change dates using either a reference file (where you can 'lift' the date from an existing file), the current date/time or a series of YEAR, MONTH, DAY, HOUR, MIN, SEC and MSEC commands. It can process files in subfolders, handles read-only files and it has a preview mode so that you can see which files will be modified. You can set file date and times right down to the 0.1 microseconds (100 nanosecond increments), or even tweak existing times up and down.

Eg 1. Set all file creation dates to Christmas day:
dirdate -CREATION date=12/25/2000 time=12:00:00 *.*
Eg 2. Add 10 minutes to file modification dates:
dirdate -MODIFIED ADD=6000000000 *.*
Eg 3. Set folder dates to the date of the oldest file. This is very handy when you copy photos to a new computer.
dirdate -r -diroldest c:\My Documents