Como você vê aqui touch -t
cria os arquivos antes de modificar o arquivo.
touch -a To change file access and modification time.
touch -m It is used to only modify time of a file.
touch -r To update time of one file with reference to the other file.
touch -t To create a file by specifying the time.
touch -c It does't create an empty file.
Outra maneira seria:
touch -d '23 August 2011 14:05:14' *.png
-d, --date=STRING
parse STRING and use it instead of current time