FCL.725 states the 6 month period from commencement and the a 6 month period post test to have the class or type rating added.
Much would depend upon your Competant Authority and future plans.
My CA have a pragmatic approach in that we will often complete ME class rating and hold the test if the candidate is going on to do the MEIR thus missing the 6 month 'time limit' and completing both Class and IR tests in the same instance, albeit still in two flights. Not had an application returned yet doing it this way.
With such a short time I would recommend to our HoT 'training as required' to meet test standard and then test and submit the application. Seems a sensible approach to me....