According to Stack Exchange API not realtime?, the API does not return results in realtime, but has 1 minute delay for the same query.
Is there a system or an app that delivers new questions in realtime for a given tag? Perhaps by email?
There is an
/events route that:
"Returns a stream of events that have occurred on the site."
He has also created a page to demo the service here: StackHose: live real-time event stream in your browser