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 storage timeframe, go to the app settings (the gear icon in the top left), then Change Security Settings.
In the smart settings, you can 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.