Generated ghost events should start generating as early as the range start minus the duration of the event.
Summary: Fixes T8347, Generated ghost events should start generating as early as the range start minus the duration of the event.
Test Plan: Create a year long weekly event, a year later, each day should have about 52 events.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T8347
Differential Revision: https://secure.phabricator.com/D13069