6 weeks should be ample time to abstain from alcohol and get a low CDT score. Please be mindful though - that post your medical on the 15 September, do not consume any alcohol until the results of the medical have been analysed and confirmed!!!!
The DVLA do occasionally compromise blood samples if they are not properly refrigerated or handled correctly in the laboratory. When this happens, some shame faced employee at Swansea will send you back to the DVLA doctor ASAP which would be very awkward if you have had quite a few cold tinnies on the night of the 15th!!!!
One to bare in mind.
CJ