The Timeline is a functionality available when you have at least one camera installed in your WiZ Home.
You can find the Home Timeline by going to the Settings page (icon on the top right of the Home page), and scrolling to the elements of the current home.

It provides every owner level user in the Home access to the timeline of all the activities which have happened in the home. This includes activities from cameras as well as listing when other sensors or SpaceSense detects activity during a monitoring routine. 

The goal is to allow you to see what happened for a given period of time in a centralised list in case you have multiple cameras, or you want to retrace all events for a given period of time all accross the home.

The home Timeline will grow with more type of information about home monitoring in the future.

You can delete events from the Timeline, and those will be deleted for all users (not only for your view).

In a WiZ Home not covered by Heads-Up, you can see activity up to 10 days in the past, whereas you can see up to 30 days in the past in a covered home.