Yestermorning

[Rihanna]

The period of time past midnight, but before you go to sleep. Its obviously past midnight, but youre goddamn sure its not tomorrow yet. Its something in-between. Its not yesterday, but it is morning. Its [yestermorning].
Not to be used in [the present]. Before sleeping, you may only refer to the present as [tomorrows] yestermorning.

[Zipporah Schumaker]

On or during the morning of yesterday; yesterday morning.