Sixth shift (2007 or later): The day of Locke's funeral.
Ninth shift: The day the hatch blew up.
Tenth shift: The day Flight 815 (whose passengers did the blowing up) crashed.
Eleventh shift: The day the same people blew open the hatch.
Twelfth shift: December 31, 2004, the day Ben moved the Island. If only Locke could have left the island at that point...
Thirteenth shift: The day Ben first arrived on the Island, in 1973.
Locke's interactions with the Man in Black in the form of Christian under the Orchid happen in 2004, as the Man in Black is not time travelling.