Backdate

[Dianne]

When you have a [school project] that you were told about six months ago, but you did it the night it was due, you backdate it by putting dating a day from earlier to make it seem like youve been [working on it] for a while. Also very useful when youre doing an [assignment] the day its due.

[Cami]

Put an earlier date to (a document or agreement) than the actual one.

[Little_Girl]

to make something, especially a pay increase, effective from an earlier time: