@HK_Aviator
Do you mean how long it takes to get an invitation to the first stage after sending your application?
For me and a few others, if you've read this whole thread, minimum has been 6 months before getting a reply/invitation to the first stage.
By "How long did it take you guys to hear back for the first stage," you mean after you have done the first stage, then @Dreamlinerwannabe is correct. Could be the same day or a few weeks till you get your results of Stage 1.
@ALKC1007
What's involved in Stage 1B can be found in this thread. Apart from COMPASS*, I don't think much has changed to the selection procedure.
*Before it was WOMBAT.