1. A display device, comprising:a real-time clock;
a video display;
a storage that stores control instructions for controlling operations on the display device; and
a control unit executing control instructions from the storage for implementing transitions between a plurality of different operation states for the display device, the transitions being based on current values of a multi-level availability flag, a level of the availability flag being periodically updated based on predefined logical combinations of current values of a plurality of flags respectively reflecting current control information related to timing,
wherein an initial value is respectively set to each flag of the plurality of flags upon an initial power up of the display device, the initial power up causing the control unit to place the display device into a standby operation state,
such that, in the standby operation state, when a Power-ON command is received and when a video display-ON signal for turning on a display of video is received by the control unit under a condition in which a date and a time shown by the real-time clock are invalid and when a value of the availability flag indicates a pending timing status, the control unit changes into a Display-ON operation state during which a control is provided to the video display to display video corresponding to an input video signal even though the real-time clock indicates an invalid status.