sorry for that, here are the detail steps.
1. Programs -> Control Panel -> Administrative Tools -> Computer Management
-> Local Users and Groups -> Groups -> Administrators -> General
See whether the credential you use to login is as member in the list
2. Programs -> Control Panel -> Administrative Tools -> Local Security
Settings -> Local Policies -> User Rights Assignment -> Change the system
time -> Properties
See whether the credential you use to login is as member in the list,
default are only Administrators and Power Users
3. Start -> Run -> RSOP.msc -> Computer Configuration -> Windows Settings ->
Local Policies -> User Rights Assignments -> Change the system time.
Look at the column on Source GPO and see whether this is any GPO name shown,
it there is, it means there is a GPO apply on the domain or OU which
overwrite your local policy. The 3rd points might be slightly difficult if
you are not the domain/OU admin because you might not able to access the
domain/OU GPO. You might need to check with your domain/OU administrator to
arrange for a modification.
HTH.