Sorry to double post but I wanted to let you know—I just noticed/remembered that when submitting your app/update, there is a "Key Dates" box on the screen that appears upon pressing Submit for Publishing. You can write the date you want the app published in this field. The description provided by Roku is as follows:
Once submitted, your channel will be reviewed and will enter the testing queue. If there are any key dates with respect to publishing we should be aware of, please enter them here. (For example, "do not publish before [date].")