It isn't quite that simple. You may be able to "get away" with different amounts of minimum training, dependent upon the attitude of your TRTO. This is because they interpret JAR-FCL differently and the CAA are hopeless, allowing inconsistent approaches to develop and not doing what they are paid for (i.e. regulating sensibly). If you ask the CAA, they will almost certainly say a minimum of 8 hours (so don't ask). In fact, if you read JAR FCL the 8 hours is in the bit that amounts to a recommendation, rather than a requirement.
However, the most important thing is to do as much training as you need to achieve the standard - this has more to do with your flying experience/currency/ability/free stick time you have managed to scrounge/ground training/skill of your flying instructor/ground work and application you make, than any purely arbitrary rule made by a bunch of bureacrats who know diddly squat about flying training. [You need to remember that JAR-FCL for helicopters was written by 30 people only one of whom had a helicopter licence].
Your first twin is a big step up and involves taking onboard a lot of new ideas and approaches to flying. I suggest it is very important that you make sure you get a real good grounding in these matters, particularly if you are to fly AOC work. Of course, this is a lot cheaper than flying time. I normally take over a day of ground school instruction just to get over an understanding of Categories/Groups/Classes etc and what they mean before even starting on the type stuff.
In the end, a sensible instructor should only let you go for test when he thinks you are ready. The enforced separation of instructor and examiner role imposed by JAR-FCL makes it more difficult for the examiner to ensure you have done enough, but that's progress!