Нашел описание формата даты на CISCO.Symbol Description
* Time is not authoritative.
(blank) Time is authoritative.
. Time is authoritative, but NTP is not synchronized
The system clock keeps an “authoritative” flag that indicates whether the time is authoritative (believed
to be accurate). If the system clock has been set by a timing source (such as system calendar or NTP),
the flag is set. If the time is not authoritative, it will be used only for display purposes. Until the clock
is authoritative and the “authoritative” flag is set, the flag prevents peers from synchronizing to the clock
when the peers have invalid times.
Table 5 describes the leading symbols that precede the show clock display.
Выходит, что время на цисках полученное по NTP не "верное". Поэтому и ставиться символ "*".