You can take SAT's when you want, the date will unlikely be reported and even if it is, I doubt they will take note of it. The best thing you can do is do well in school but most importantly do EXTREMELY well in your SAT's, specifically math.
Also, I wouldn't worry too much about EC's. I didn't have any and still got into Yale, Stanford, Penn, Princeton so personally I wouldn't worry about doing any more then what you already have.
Your goals should be at least 3 A's in your A levels and 700+ in your SAT math.