Hey, I made a small revision to my Greasemonkey script that makes it smarter about handling time (particularly AM/PM).
It's updated here and updated on Userscripts, where I'm up to like 566 installs! I'm a hit! Or something. And I'm like the 4th link in Google if you search for "google calendar evite!"
If you've got Greasemonkey, install your Evite to Google Calendar script right from here.