This app uses timestamp strings from the JSON data stored in a field named lastupdated. The timestamp is used to determine whether or not to update cached data stored on the end user's device. If you modify your timeline node data, you should update the lastupdated value. This will refresh the end user's cache and they will see the latest version (not an older cached copy of the data). But, you can't just add your date string in any format you want. The date timestamp in the JSON file for Vanilla Timeline has to be in ISO 8601 format which looks like this:
In your JSON file, the date string should look like this: "lastupdated": "2026-01-01T00:00:00.000Z",