Pressman helping Riker is exactly what I was touching on. To me, Pressman came off as a guy who would reward loyalty. I'm very much under the impression that Riker didn't really fully understand why he was technically in the wrong till years down the road.
As far as the four year thing goes --- that's generally backed up except where Beverly is concerned. According to Memory Alpha, she was there for 8 years, which doesn't exactly jive with Julian only being there for four. However, the discrepancy might be explained away by there being an additional 4 years between Julian graduating and being posted to DS9.
Additionally, according to Memory Alpha, Barclay was offered the commission for Lt. without going to the academy, instead, he got his masters in Computer Systems from the Daystrom Institute. He was there for 8 years.