With server-side includes. Ask your webmaster if this is
supported, and what the exact syntax is for your server. But
this will display the local time on the server, not for the
client. And if the document is cached, the date will of
course be incorrect after some time.

JavaScript can be used to display the local time for the
client, but as most people already have one or more clocks
on their screen, why display another one?