dormantsrule, if you've submitted other banners, you can look to see when they are scheduled to run. In the banners forum, click on the "Upload a Banner" link on the right side. There you can see any banners you have submitted. They will be labeled things like "Awaiting Approval," "Approved" and "Approved for (date)." I like to mark on my calendar when one of my banners is scheduled to run, just to be sure I don't miss it! I think Dave changes the banner around 6 pm, so if your banner is scheduled to run on, say, January 22, it will be posted on the evening of January 21st, and will stay up until the evening of Jan. 22.
Hope that helps!
Angie