Ok , I just went back to PD and tested again.
By the way I have PD version 6.00.1604a What do you have?
Go into Create Disc.
Click on the Spanner Icon at the foot of the page
In Create Disc Preferences - Menu
Uncheck Enable Video Thumbnail and then click OK
Goto Preview
There should be no animated preview
(this might be what you want)
Go back to Author
Click again on the Spanner
In Create Disc Preferences - Menu
Check Enable Video Thumbnail and
Set the time user-defined menyu to 40 seconds
and then click OK
Goto Preview
It should run the animated menu for 40 seconds and then re-cycle
In the Actual DVD when burned I bet it runs for 40 secs and then runs the Fisrst Chapter of your video
If you can't solve the problem - Change the problem