Could you not just configure the snapshot retention period for each volume using system manager? In CDOT you would just create a SnapShot Policy and assign the volumes to it. In 7 mode just use set the retention to 6 daily and 1 weekly. You would not have to run a script everyday for this. If you have a lot of them you could use powershell to assign a policy to all of the or DFM "Run Command".