Were you able to get this worked out. The script that was suggested was referring to an older version of iCal and I can't seem to get it to work in the newer iCal where the checkbox is for "turn off all alarms". I changed the settings thinking that I could make it move to the correct checkbox but for some reason, it jumps over that checkbox. Any advice is welcome.
My iCal is up to date in OSX Lion and the script below is working for me. It doesn't actually take time into account, like beckmart had wanted and I'm not very applescript savvy so I just put it into an automator workflow using the script twice with a "pause" in between.
tell application "iCal" to activate
tell application "System Events" to tell process "iCal"
click menu item 3 of menu 1 of menu bar item 2 of menu bar 1
click button 3 of tool bar 1 of window 1
click checkbox 1 of window 1
click menu item 10 of menu 1 of menu bar item 3 of menu bar 1
tell application "iCal" to quit