I would disagree on that. If you only want to schedule publication of some of your pages, you would not expect anything to appear in these fields on pages that have been published manually. In contrary I think it is misleading this way, because it looks like the publication had been scheduled, although it was not. I think it is much clearer if the fields give a clear indication of the user's intention:
Blank = nothing happens
Filled = publish/unpublish at this date/time
Imho the page status is handled by PW and editors should be aware that they can publish and unpublish pages manually. Your module is a great addition, but in my eyes it should enhance the core functionality by offering a way to schedule publishing/unpublishing without forcing additional actions or altering page data.
Maybe it would be a nice addition to show a status in the fields that informs the user about the effect of the module like that (in an InputfieldMarkup or as description of the fieldset):
Page is currently PUBLISHED, no settings have been applied
Page is currently UNPUBLISHED, will be published on XX.XX.XXXX – XX:XX:XX
Page is currently PUBLISHED, will be unpublished on XX.XX.XXXX – XX:XX:XX
You could even make it really fancy and include a countdown or something like that.
This is of course just a quick thought and I do not want to "order" new features. I just wanted to address the user experience aspect and make a suggestion how it could be improved.