The company I manage has recently employed a 457 worker. this is the time line that is took us.
5 weeks for the company to be approved 457
3 weeks to get the position approved.
The employee is already on a 457 in australia and his stuff was put in at the same time as getting the position approved, he starts next week.
We used a very good agent that had it all correct first time.
I originally came on a 457 and it took 5 months because the employer did not use an agent and thought he knew what he was doing, it was like ping pong.
I think it does depend on the application being correct and obviously you don't have to use an agent just have to know what you are doing.
I recently went to a mining exhibition and immigration were there. I spoke to the lady and she said that from june (I think) it will be easier to change from a 457 to PR as you will be able to use existing documents provided for your 457 visa.
Hope this helps
Martin