Not sure exactly what you are asking
Incrementals are based on whether the Archive Bit has been set. If it has then the file is backed up and the bit reset. (Differantials are similar, but the bit is not reset)
If you are backing all files changed after a given date, then you'll need to re-save the Selection List every time you change the "as of" date.
If you are backing up files changed in the last xx days/weeks, theh the list should not have to be changed