You can't set the clock with a securelevel of 2 or higher, from
init(8):
Code:
The kernel runs with five different levels of security. Any super-user
process can raise the security level, but no process can lower it. The
security levels are:
[...]
2 Highly secure mode - same as secure mode, plus disks may not be
opened for writing (except by mount(2)) whether mounted or not.
This level precludes tampering with file systems by unmounting
them, but also inhibits running newfs(8) while the system is multi-
user.
In addition, kernel time changes are restricted to less than or
equal to one second. Attempts to change the time by more than this
will log the message ``Time adjustment clamped to +1 second''.
You will need to boot in single-user mode and set the clock, or use a rc startup script and reboot.