Hi, when I last asked Microsoft this was the answer (~16mths ago):
Q: Do watchlists expire or remain forever?
Watchlists - List - REST API (Azure Sentinel) | Microsoft Docs has a properties.defaultDuration (which seems to be 1day 3hrs) but what is it there for / actually do?
Answer:
This is a future capability, currently not active
If this answer helps, please Accept.