I got annoyed with the fact that iCal only contains a few options for how often it will auto-refresh subscribed calendars, especially since the lowest interval is 15 minutes. We are publishing and subscribing over a LAN, so no worries about bandwidth; we wanted updates at most every two minutes. If you also want to change the refresh interval for subscribed iCal calendars, it is dead easy:
<string>~/Library/Caches/com.apple.iCal/Indexes/cal_name.index</string>
Where cal_name is the name of the subscribed calendar. Somewhere below that line, you'll find:
<key>automaticUpdateInterval</key>
<integer>900</integer>
Change this value to your desired refresh interval (in seconds) - I use 120 (two minutes).
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http://hints.macworld.com/article.php?story=20040515062644352