Remember that touch will update the file relative to "now" instead of the existing date stamp on the file. Also, the -d option to touch can take the exact same information as the -d option for the date command. The -r option will make touch work relevant to the existing time stamp of the file. So, what you want should just be this 'touch -r file -d "+14 hours" file' as thus:
$ ls -l test; touch -r test -d "+14 hours" test; ls -l test
-rw-r--r-- 1 matrixm matrixm 0 Mar 27 04:17 test
-rw-r--r-- 1 matrixm matrixm 0 Mar 27 18:17 test
The -r option requires a filename to operate against (I discovered this during my testing while writing this up), so you need to list the file twice. You should be able to use a for loop, replacing both calls to the filename with a variable instead to quickly do all of the files, just be careful of your regex so that it doesn't accidentally catch files with the correct timestamp already (I always merely output the resulting files of a regex with an echo command before continuing writing a file modification loop). Unless, that is, you have the files that need the timestamp modified in their own directory. If that's the case, then you could do:
for FILE in filestobemodified/*; do ls -l $FILE; touch -r $FILE -d '+14 hours' $FILE; ls -l $FILE; done
I would suggest holding off on running that one liner until you know for certain that the touch command with the -r and -d options will give you the result you want.