There are LOTS of threads in the forum about release.
Short answer is that the release occurs before impact and finishes after. In TGM terms release means an out-of-line condition seeking it's inline state (eg. straightening right arm). The sequence with which the accumulators release is different for hitters and swingers.
Some searches should give you more detail. I recommend starting with the oldest posts first, as you'll find some really good stuff from Yoda in the archive forums.
If you find any old threads that helped clarify for you, please post links to them here so future seekers can benefit!
To be honest - I felt like drowning looking at hundreds of posts/threads, so I went for the quicker solution to take it up here once more. In addition I had the Martin Hall / Jack Nicklaus card that I thought gave it a new take?