10m normal: 30 per week, 9 weeks to complete. heroic: 42 per week, 6 weeks to complete
25m normal: 42 per week, 6 weeks to complete. heroic: 60 per week, 5 weeks to complete
Now, in adding these times up, I did not suggest completing the quest and starting the next phase in the middle of the run. If you were to try to be as efficient as possible, turning in as soon as you were done and starting the next phase mid run, you might shave a weeks off the entire completion time. I am looking at 16-17 weeks to complete (phase 2 and 3), 11-12 weeks if we could kill all the bosses on heroic 10m. 25m normal is about 8-9 weeks.
Overall, i do not expect to complete this before the next expansion unless Blizzard changes the quest chain.