I wrote a program to do that a few years back. It would create a filename using the current date. It was easy to set the parameters of the backup to whatever files I wanted to save in the backup. I will try to find it and make it available.
I do remember looking for a program to do it and did not have much luck.
It also turned out to be harder to write than I expected... About 8 pages...
I'll check around for it.
Sorry, I just re-read your post, you want to run your DOS backup on specific dates not include the date in the filename...
Do you want this to be a TSR terminate and stay resident?
Are you planing to put this into the autoexec.bat and check the date on boot?