Each event fact will have a "Sort date" field that will be automatically filled based on the date of the event listed. When you have 2 or more dates the same use -x to signify which is first, with x as a 1, 2, 3, etc. Any sort date without a dash will be sorted after those with a dash.
12 May 2010-1 (for the first event)
12 May 2010-2 (for the second event)