cp /etc/inet/ntp.server /etc/inet/ntp.conf
edit the ntp.conf file.
add server(s), for example:
server 0.be.pool.ntp.org
server 1.be.pool.ntp.org
server 2.be.pool.ntp.org
server 3.be.pool.ntp.org
svcadm enable svc:/network/ntp
SysAdmin: How to configure NTP on SUN Solaris 10.