Start from the constraint, not the convenience. List every participant's city, then look at where their working days overlap at all. With three continents involved there is usually one narrow window, and it is better to find it deliberately than to propose times and iterate over email.
A repeatable approach
First, put all participants on one timeline and identify the overlap. Second, rotate the inconvenience if the meeting recurs — the same person should not always take the 6am call. Third, always send the invitation with the time zone named, and let calendar software convert it. Fourth, confirm the date, not just the hour, when the date line is involved.
The meeting planner on this site does the first step for you: add each city, set your working hours, and the shared window is highlighted.