not strictly true my friend, we have the January window as well, as STCC looks across the whole financial year to end of May 2017.
Yes I made a grave error in my first post, as you know I was curious as to the actual cut off point, with further research it would seem that clubs submit the projections on 1st March.
In the Premier League, any overspend is assessed during 'T' (with all clubs required to submit projected figures for the current season by 1 March). Because the current season hasn’t yet finished, this March submission includes a forecast for the financial loss (or profit) that the club expect to make during ‘T’ (i.e. this season). This March submission, also needs to include the actual figures for profit or loss that they made in the two previous season (T-1 and T-2). Total losses are therefore assessed over three seasons (T, T-1 and T-2).
http://www.financialfairplay.co.uk/latest-news/2015-16-premier-league-profit-sustainabiltyrules