dead of night
The middle of the night. Why are you calling me in the dead of night? Can't this wait till morning?
dead of winter
The middle of winter, which is usually especially cold. I find myself dreaming of tropical islands every year in the dead of winter.
dead of night/winter, the
The time of most intense stillness, darkness, or cold. This usage dates from the sixteenth century. Shakespeare had it in Twelfth Night (1.5), “Even in the dead of night,” and Washington Irving used the alternate phrase in Salmagundi (1807–08), “In the dead of winter, when nature is without charm.”