Hi Tom,
The extension will send out the newsletter at the first chance it gets where the set time frame has elapsed (since the last send). This means, for example, that if you enable it on a Sunday, and set the `Start Date` field to that day, it will most likely send the newsletter on that Sunday. Then, one week later, when it checks on Sunday, it will see that more than 1 week has elapsed and will send again.
If you would like to guarantee more regular mailings, you should set the `Start Date` field to the first day you'd like the mailer sent out. Then, set up an automated task (`cron`) to visit your website early in the morning every day. See
www.tnrjoomla.com/index.php/Latest/Documentation.html for more on that.