These are the five computer time protocols I recommend providing. For SNTP/NTP, use OpenNTPD (note: if you’re using Solaris 10, check this page for using OpenNTPD Portable with SMF).
SNTP v. 4
RFC 2030
UDP port 123
NTP v. 3
RFC 1305
UDP port 123
Daytime
RFC 867
TCP/UDP port 13
TAICLOCK
http://cr.yp.to/proto/taiclock.txt
UDP port 4014