At least two webpages exposed me to Google’s New Feature for Gmail entitled Gmail Custom Time.
The feature allows you backdate current email to make it show up in the recipient’s email inbox as if it were received on that specified earlier date.  You can even choose to have email appear as read or unread in the recipient’s inbox.

The deadline-oriented lawyer in all of us can see the dangers if this feature were real.  For those who have missed deadlines (and have little regard for ethics), this feature is sadly Google’s April Fools’ Joke for 2008.