One way you CAN do this, in a round about way, would be to have two page bodies in your field group - basically old and new - and a date field associated with the “new” page body. Then within the template that displays that content, use a conditional like:
{if new_date < current_time}
{new_body}
{if:else}
{old_body}
{/if}
Granted, that’s a cheat really and not actually updating the entry on the specified date, it’s simply swapping version one for version two.
If your content was accessed by template group or template name and didn’t reply on the entry’s URL title, then you could handle it with two distinct EE entries and simply expire one and publish the second at the same time. But as soon as access to that content is dependent on the url_title segment, that doesn’t work because of the requirement that each entry in the same channel has a distinct url title, and so your url for entry 2 could not be the same as entry 1.
Sounds like you’ve come up with an interesting case for an add-on that stores a scheduled update to an entry.