Hi thelaurakate,
We placed our visa application 1 month after the nomination. Technically, you don't have to wait to submit your application until the nomination is approved. You can (and a lot of people do) even submit your application on the same day as your nomination or any time after that. But I know that some people choose to wait until the nomination is approved for a number of different reasons. Such as, they don't want to risk the hefty application fees in the case of the nomination is refused. Or they are not in a rush and don't mind waiting a little longer.
We decided not to wait. One of the reasons was that our visa was about to expire at the end of November and we had to apply to get a bridging visa. Also, my partner's work have sponsored a number of people in the past and they were submitting another 457 visa at the same time with our 186, so we didn't really have any reason to worry about the outcome and losing our application fees. And, we just didn't wanna wait 4+ months for nomination and then another 4+ months for our PR. In hindsight, I wish we'd applied on the same day as our nomination - the waiting is killing me!
We didn't use a MA and we are in Victoria, in case you're wondering.