ASCII string of format:
yy/MM/dd,hh: mm: ss±zz
or
yy/MM/dd,hh: mm: ss
or
yy/MM/dd,hh: mm
yy - 2-digit year [2000-2069]
MM - 2-digit month [01-12]
dd - 2-digit day of month [00-31]
hh - 2-digit hour [00-23]
mm - 2-digit minute [00-59]
ss - 2-digit seconds [00-59]
zz - (optional) time zone offset from GMT, in quarter-hours [-47...+48]. If
this value is not specified, the time zone offset will be 0.
Example:
AT+CCLK=?
+CCLK: "88/12/31, 23: 59: 59(-47-+48)”
OK
AT+CCLK="01/01/01, 01: 01: 01-06"
OK
AT+CCLK?
+CCLK: "01/01/01, 01 : 01 : 01-06"
OK