If there is at least one camera in your home, the events remain visible on the timeline as long as the corresponding video is stored on the memory card of the camera that recorded the event.
With or without a camera in your home, the event storage time is limited to 6 months for all products in your home.
By default, this period is set to 3 months. In most cases, the camera's memory card will be full before the 3-month mark.
To change this time, go to the Home + Security app > Settings > Change security settings > Smart settings > Delete old events.
You can then choose to delete old events after 48 hours, 1 week, 1 month, 3 months or 6 months.
You can find more information about the memory card here.