There are date and time parms on the SAV command. You need to do F9 for all parmeters to see them
SAV DEV('/qsys.lib/tape.devd') OBJ(('folder/path')) PATTERN(('*' *OMIT)) CHGPERIOD(mmddyy hhmmss mmddyy hhmmss)
You can use “SAVCHGOBJ” to backup only the objects changed between backups (use update history *yes). This will allow you to back up only the new files added. I would recommend that you do a complete backup and then you can get rid of the daily backups.