Get/Set the system time of the device.
The input format is 'Year-Month-Day Hour:Minute:Second'.
ex: 2011-01-01 05:43:05 means 2011/1/1 - 05:43:05 .
The value range:
Year : 2010 - 2090,
Mouth : 1 - 12,
Day : 1 - 31,
Hour : 0 - 23,
Minute : 0 - 59,
Sec : 0 - 59.