If you are sure that you’ll only ever use the first row of the repeater then the meta key for your first date sub field will always be event_dates_0_event_dates_date
As a side note, because of the way ACF names field you don’t need to name your sub field event_dates_date and you can just shorten that to date and this would result in the first row always having the meta key of event_dates_0_date
