First of all, I thank you for replies to my question.

Here is the summary of how to set time.

        1) Setting local time zone.
                # rm /etc/localtime
                # ln -s /usr/share/zoneinfo/Japan (or your local time zone)

        2) Setting GMT bias (in the booting menu of the booter)
                GMT bias is the number of minutes east of GMT.
                In my case (lives in Japan), the GMT bias is +540 (+9 hours).

Let me make some comments.

  There was a trap at least for me. The time in my MacBSD was 14 hours fast
against our local time, because the default GMT bias was -300 (-5 h) and
the local time is JST (GMT +9h).  To adjust the time, I changed the GMT bias
to +540 (+9h) and rebooted my MacBSD. But There was the following warning.

        Warning: Battery Clock has earlier time than UNIX fs

And the date command displayed the wrong time ( I guess this was the last
shutdown time).  I had to wait for passing about 14 hours.

  I rebuild some kernels with different timezone setting and tried them. But
it seems that the timezone in kernel configuration file is nothing to work.