I’m fairly certain that the calendar is the same - June 15 after their sophomore year, so that would be partway into your son’s Year 11. Also note that men’s rowing recruiting is, in practice, later than that - while there may be some communication earlier, the significant majority happens between spring of junior and fall of senior year (on the US schedule).
That said, I’m sure there are intricacies that I’m not familiar with around international timelines, and you may want to consult a professional, if only in a limited way.