When an author publishes an article, it immediately becomes visible on the web site and will be tweeted pretty soon after. The following day it'll be included in the automatic email digest for all email subscribers.
If authors post their articles on random days, the email subscribers will get emails on many days of the week. This will lead to frustration over the volume of emails, and will lead to the club's messages being ignored and not read.
So, we have a publishing schedule whereby all but the most important messages are published on Monday so that they are automatically emailed on Tuesday. Our authors can write their articles on any day of the week and can specify the date that their articles should be published.
For your further information, the automatic emails are sent by Google Feedburner between 7am and 9am and they include all new articles since the last digest was sent. No email is sent on any day when there are no new articles!