I think what K Biermann is refering to, are the Time Machine snapshots, not the snapshot apis for third parties. My experience has been the same. The time machine snapshots last only for around 24 hours.
According to the support article https://support.apple.com/en-hk/HT204015
"
- A daily snapshot is saved every 24 hours, beginning from the time you start or restart your computer.
- A weekly snapshot is saved every week.
- Starting with macOS High Sierra, an additional snapsnot is saved before installing any macOS update."
This doesnt happen with my snapshots, or with any other High Sierra mac I have checked.
At most there are snapshots for the past day. So no daily snapshots beyond 24 hours, absolutely no weekly snapshots either. This renders the feature much lesss useful for me.
I would like to understand why time machine is so aggresive in deleting old snapshots, even when huge amounts of drive space are available.