The deadline for appealing to the Upper Tribunal is one calender month from the date that the statement of reasons is sent, so you don't need to worry about missed deadlines until you receive it.
From what I can remember, the argument that a very late statement of reasons amounts to an error of law has been tried, but failed at the UT, although the UT Judge did accept that an SOR that takes an exceptionally long time may lose credibility.
