Automatic
When Automatic is selected and you have Accepted the event invitation, location sharing will start at the date and time specified in the Event Overview screen.
Manual
When Manual is selected, and you have Accepted the event invitation, location sharing will not start at the date and time specified in the Event Overview screen. To start location sharing at that time, you will need to tap the red Start Location Sharing button, then confirm a second time before location sharing will start.
In both Automatic and Manual mode, location sharing will run for the duration of the event unless you change your status to Tentative or Declined at which time location sharing will stop.
See also: