Most centres including mine get students to complete the EPQ for March of year 13, meaning you get the grade alongside A2 results. I assume unless you are doing yours over the two years you will submit it March/April time ready to be marked around this years exams. Your supervisor is probably better to ask as all centres work differently.
However, I do think submitting it when all your teachers think itll be a D is a waste of time. EPQ is only useful if you get a A or a B at a push in order to get lower offers. A D will only provide you with a small amount of extra UCAS points.