Yes the 5 on 3 off are as advertised. If you are called to work on a day off you can refuse, if you do work its £212 plus your normal sector pay. Doesnt happen very offen though as you can imagine!.
Speaking from my own summer roster earlies start on average with a 530-600 report and finish about 1500. Sometimes a little earlier sometimes a little later.
Lates start anywhere from 1230 to 1700 (usualy closer to 1230!) and finish 2200- 2315.
Standbys are on average 2-3 days a month but I am usualy called in on them, but thats extra sector pay as opposed to none!
I find I get tired on earlies but the shifts are fine and as you say there is a huge advantage to being able to plan you life.