It takes Bioware 5 months for 1 new Op. Is that a good estimate?
No. They surely have different teams working on different things. For example, one team working on the new OP, one team on the new WZ, one team on f2p, one team on Maked, one team on HK and so on.
It's not that one team does the OP and then does the WZ and then does the f2p and so on.