190 for Ships officer EOI invitation

I am going to apply for EOI for ships officer, usually how long it takes to get invites for NSW or NT?
Its quite a rare anzsco, hard to say mate, but the indicators are: if your aznsco is rare than higher of invite with NSS is generally higher.
Thanks for your reply mate. I didnt understand this part" if your aznsco is rare than higher of invite with NSS is generally higher", it will really helpful if you explain this part.