The "Entry Date / Publish On" field is the official entry date and time displayed with the entry on your weblog using the MTEntryDate tag. In reality, it is the time at which you began writing the entry.

Movable Type allows you to edit the date and time in order to pre-date or post-date your entries. If you change this value, it must be in the form of YYYY-MM-DD HH:MM:SS.

Note: The "Authored On Date" field is hidden on the default entry compose screen. Customize the compose screen settings using the "Customize the display of this page." link at the bottom to add this field to your compose screen.