You can approximate this behavior by fiddling with the Stack Exchange API
For instance, this query will return the number of posts from 9-27 to 9-28 (today).
Now you can fiddle around with this query by fiddling with the date amounts. For instance:
You can change the
fromdate (which is in UNIX Epoch Time) to something better (last hour, last 6 hours, whatever).
The issue is that API calls are heavily cached so they may not be up to date (my query to show all posts from the last 30 minutes returned a zero), and using the API in this way may be considered abusive under the terms of service depending on how and how often you use it.
I think the bigger question is why on earth would you want that information?