Try this.
Create a calendar entry in Notes
In my example, I created it while in EDT timezone, but the entry was for 7:30 AM CEDT start and 8:40 AM BST end
Export it to ICS format
Import that entry into Apple iCal (NOTE that the times are incorrect)
…not sure if this is an iCal problem or Notes problem.
See the calendar .ics file below
Subject: iCal exports
Hello Tim
I have had some issues with the .ics files - as I manually export each and every cal entry from my Notes Client to my desktop and then import to my iCal. Then I sync it to mobile phone. Yes at least 4 a day.
In the iCal Preferences there is Timezone support - this addressed my issue when I enabled it. However Getting it to default to the correct timezone is a challenge in itself 
Subject: this is known iCal ics interop issue