This is is a wonderful metaphor: "looking in the fridge every few
minutes and hoping that something tasty will appear".
I may be thick, but Planet does not appear to store any information
about how often a feed ought to be polled (my blog seems to be hit
every 20 minutes even when I'm AWOL). I use rawdog, which does.
When adding a feed, I make a vague guess at how often I want to
poll it, and then periodically adjust the time based on how often
updates actually happened. This is done with a terrible, awful, ugly
hack that reads the database and spits out the config file
with new-and-improved times. Pretty dumb, but good enough "for now"
(apparently I haven't touched it in over a year).
rawdog will also automatically update feed locations if given a 301.
Since it already rewrites the config for that, I might try to merge time
updating into the core someday, but no one has demanded such a feature
AFAIK.