Currently the publish newsletter script will publish at any time including the past. There should be a block that prevents the newsletter from publishing in the past.
Another option would be to add a confirmation if you want to publish within 1 hour of the script's run time. This will help catch mistyped values.
Finally, there should be a visible confirmation that the script was ran. This will show the time so that folks can make an update in the event that a mistake was made.