Unfortunately I have to deny this request: The function to set folder timestamps isn't currently supported by tcmadmin.exe, and it would be too much work to add it, sorry.
This can happen when the user under which TC is running has the right to access the folder. Currently the function to get/set the folder timestamp isn't impmemented in the tcmadmin tool.
Maybe in a later version, but it will need a lot of changes to the main copy function. Since this is more or less the core of TC, I don't want to change it in a minor release - the risks are just too high.