It should work with double quotes too, my test above did.
BTW your quoted code above can get you inot difficulties if any variables accidentally cooincide with the terms
ADD DATESTRING '"Wednesday 30 November 2011"' ENDDATESTRING '"Wednesday 30 November 2011"' TIME '"11:00"' ENDTIME '"12:00"' TITLE '"lunch break"' NOTE '""' REPEAT '"1"'
would be better as
'ADD DATESTRING "Wednesday 30 November 2011" ENDDATESTRING "Wednesday 30 November 2011" TIME "11:00" ENDTIME "12:00" TITLE "lunch break" NOTE "" REPEAT "1"'
(NB the whole string is srrounded by sigle quotes not just the arguments)
in your above 'ADD' 'DATESTRING' etc etc will get replaced by any variable in your script with the same name. Either you have to be very careful about variable name choice or simply quoting the command saves the risk.