What is the latest time by which final assessment is required to be made?

The final assessment order has to be passed by the
proper officer within six months from the date of the
communication of the order of provisional assessment.
However, on sufficient cause being shown and for reasons
to be recorded in writing, the above period of six months
may be extended:
a) by the Joint/Additional Commissioner for a
further period not exceeding six months, and
b) by the Commissioner for such further period as
he may deem fit.