If you call before then, the IRS will likely politely (ahem) ask you to call back later.

FORBES: The Month After: Refund Status, Lost Checks and Tax Planning

Hiring managers might hang up instead of ask you to call them back.

CNN: Are you unemployable?

Something tells us, however, that the doctor won't ask us to take two dubstep tracks and call back in the morning.

ENGADGET: MIT ear-powered wireless sensor sustains its charge through sound