Currently, Podcast can be checked for updates at intervals of one hour or more. For podcast feeds containing news (or other current information) this is imho not ideal.
Some of those (see my examples below) are published on a very irregular basis, but a lot of times each day. I guess 15 Minutes intervals are the highest appropriate in such a case. The less the better, I think.
Other podcasts are published on a very regular basis as e.g. every hour at minute 00. For those Feeds a specific point of time would be good for retrieving, e.g. "at Minute 05 of every hour".
For not to overload servers I suggest to offer shorter intervals only in the podcast feed specific settings, but not in the general podcast settings (so it would only be available for the podcasts where needed, but not used generally).
If you like examples, please see this ones:
- http://www.tagesschau.de/export/video-p ... -sekunden/
- https://fapi-top.prisasd.com/podcast/pl ... etines.xml