The Send Later plug-in for Mozilla Thunderbird (http://www.unsignedbyte.com/?page_id=4) lets you customize the times at which your emails are sent. When you are sending an email, you can invoke the plug-in to tell it exactly when you want the email sent, or you can select a delay relative to the current time. This is a great extension for making your boss think you are working while you are off doing "other things" :)