You must have appropriate privileges to set the system clock. For changes to persist across a reboot, the hardware clock may need to be updated from the system clock, which might not happen automatically on your system.
To set the clock, you can use the --set (-s) option
(see Options for
date). To set the clock without using GNU
extensions, you can give
date an argument of the form
‘MMDDhhmm[[CC]YY][.ss]’ where each two-letter
component stands for two digits with the following meanings:
day within month
first two digits of year (optional)
last two digits of year (optional)
Note, the --date and --set options may not be used with an argument in the above format. The --universal option may be used with such an argument to indicate that the specified date and time are relative to Universal Time rather than to the local time zone.