I live in France and have an international client base. All sales are displayed in Paris time zone, which is UTC+1.
Time Zone differences can change with the seasons depending on when a country adds and subtracts an hour in the spring and fall. (It isn't always the same date from country to country!) I try to always let a sale last long enough for the West Coast in America to have a full day on the last day of the sale.
Find your Time Zone in relation to France (UTC+1), here: World Time Zone
Something to keep in mind:
If a sale starts in the morning in France, it will actually start during the night before in America.
Sales usually start in the afternoon in Australia.
Since I let the sale go until midnight PST the last day of the sale, the sale will actually end the following morning in France - the following afternoon in Australia.