If you want the amount of disk space consumed by all Snapshot copies to not exceed a certain percentage of the used disk space, use the cumulative values in the snap list output to determine which Snapshot copies to delete.
If you do not want more than 5% of used disk space to be spent by Snapshot copies, delete all Snapshot copies listed below nightly.1 in the snap list output; that is, nightly.2, nightly.3, and nightly.4. After deleting the Snapshot copies, nightly.1 and all the other more recent Snapshot copies consume 5% of the used disk space.