Not sure how it goes in Primary, but in Secondary I was awarded around a third of the time that I worked towards my probation.
This was about 7 years ago mind you, I was the last year that qualified before McCrone came into effect.
The argument was that I wasn't teaching enough "subject specific content" as there were limited certificate candidates, surprisingly...
As I say, only my experience, and it was a (worryingly) good bit ago.
Sorry I can't be much more help.