coding and testing pipeline

This is one good Agile/Scrum concepts which is rarely used in most of the teams. I recommend using it even if your working "waterfall".

Instead of releasing the full feature set for testing on beta /hand-over-to-test day, you need to have small releases , each one both stable and has additional testable feature.
Benefits:

1. This will allow the test team to start testing even before the regular date (more time to test means more bugs are found)
2. reduce the instability of the version , which save time for both developers and QA.
3. Allow faster feedback on bugs for the developers.
   

There should be be multiple releases in each version. Don`t go to far and release one each week (remember that it has an overhead which can never reduced to zero, no matter what the "Agile" methodology says).
I believe a once-in-month period is sufficent , for a 3 months-version perioid.