Int 1Ah, 0Bh            Set System-Timer Day Counter                 some XTs

    Sets the number of days since January 1, 1980 for the System-Timer.

        Entry   AH = 0Bh
                CX = Number of days since January 1, 1980

        Return  CF   Set if error; else cleared

    ──────────────────────────────────────────────────────────────────

    The system timer is the timer set when the system is started. This
    date is temporary, lasting only as long as the system is turned
    on.

    This service is available only for XTs dated 1/10/86 and later.
    ATs and XT-286s will set the Carry Flag, thus reporting an error
    state. Previous machines will report unpredictable results
    (including the state of the Carry Flag).