User Configuration > Administrative Templates > Microsoft Project 2016 > Project Options > Calendar
User
HKCU\software\policies\microsoft\office\16.0\ms project\options\calendar
Specifies the start time that Project assigns to tasks by default when you enter a start date without specifying a time. If you enable this setting, new tasks where the user does not enter a start time will use the start time that you specified. If you disable or do not configure this setting, the user's default setting is used.