Postfix feature # 20051103 added the following (from the 2.3.13 release notes):
Better insight into the nature of
performance bottle necks, with
detailed logging of delays in various
stages of message delivery. Postfix
logs additional delay information as
“delays=a/b/c/d” where a=time before
queue manager, including message
transmission; b=time in queue manager;
c=connection setup time including DNS,
HELO and TLS; d=message transmission
time.
As I would suspect, the longest delay in your setup is being caused by connection setup, DNS, and the initial SMTP conversation. Seems normal to me.