I'm thinking some here are confusing back ups with version control, these are two different subjects all together, a back up is a 'copy' of the master so if you want to back up your master file, whether it's not the master in your project or not say is irrelevant here, comparing time stamps is surely good enough. If your updating your source for version control that's different.
Mick:
Comparing time stamps for backups is not good enough for anything because as I've stated before comparing time stamps allows for the "backup" file to be a newer, but wrong, version of a file. This has nothing to do with version control.
To prove my point create two folders somewhere on your computer named "master" and "backup". Drop some files in the "master" directory and run Tim's routine to backup the files from "master" to "backup", which should work quite well. Now go in the "backup" directory, open a file, erase something, save it and go run Tim's program again. How well does that work out? Not well I'm going to assume as his program is only checking if the file in the "master" directory is newer than of that in the "backup" directory, which is 100% the wrong way to do it as I've just proven.
If you think to yourself "well that's stupid because no one will ever be able to access my backup folder other than me so they won't be able to change the file". This again is the wrong assumption. To prove my point open a file in a text editor, even if it's binary, and add "q" somewhere in the file. This would be a representation of a corrupt file in which the backup method would fail.
This is not a version control method but a method of verifying file integrity. Ensuring that your backup is exactly that, a backup, not just the most recently edited version of a file. Tim's code may work flawlessly until the end of time, but one day he may go reaching for a backup file and find out he's screwed.
This is the exact reason that a lot of open source software offers a checksum along with their downloads, so you can verify that the file you obtained is exactly what they intended to provide as a download. Open Source is not all hippies and beards, there are a lot of smart people hacking away at different things and a lot can be learned from observing them.
Note: The last paragraph was not directed at you as I know you follow a lot of open source stuff, it was merely a general statement directed towards those who live in their own little coding world without doing some exploration.