Exch Admins can play with these settings. Adjusting when the queue runs is one option, but you could be unlucky and hit send when there's a small queue that's running in 10 seconds. I think admins can also force a delay, which is a different operation than spooling it for the normal SMTP process.

Outlook/Exchange users can also delay sending (though reneging may take an admin to do): http://www.tech-recipes.com/rx/1638/how_to_delay_sending_mes... . Gmail needs this feature badly!

Handy if you'd like to compose a announcement early or appear to be working hard at 6 when you really left early to hit the links :)