I see that new questions appear for a certain tag, but there is no RSS feed for that. How often is the feed updated or how long must one wait for RSS to send a notification?
If you're looking for a feed that can be refreshed once per minute and contain up-to-date information, I recommend a small tool I created called stack2rss.
It converts API requests into RSS feeds that can then be subscribed to.
An example that displays all new questions on ServerFault tagged with