yeah the default retention is 30 days, but once you update it from the UI it will be updated.
Also the change you make in the UI will only be for the newly ingested data, so if you have data for last 5 days which had old retention policy then will be deleted after 30 days, this is done as updating old data is a resource intensive process.
on a side note please give more than 4 hour retention, clickhouse does merges every 4 hour.
https://clickhouse.com/docs/en/operations/settings/merge-tree-settings#merge_with_ttl_timeout