Changing date created of bulk files to 9 hours before
To do that, you need to open the 'Terminal'

In your Terminal, enter the following command:

touch -t YYYYMMDDhhmm.ss (DON'T press enter yet)

replace YYYYMMDDhhmm.ss by it's respective characters

So for example:
touch -t 197512232000.23 (DON'T press enter yet)

Locate the files you want to change their timestamps in Finder

Select all the files you want to modify and drag them into your Terminal and now, press enter

The timestamps are now changed.