On p17 of the presentation they have commentary on stage 2...

On p17 of the presentation they have commentary on stage 2 development, and yes they do say
     • Commissioning in H2 CY20 
But then they qualify it with a footnote
    1. Subject to current review

Looking back at stage 1, they announced start of construction at 22/11/2012 but were largely tied up in site establishment works - building roads and the camp until March 2013.
They were filling their first pond in Sept 2013.
They began commissioning the liming plant in Dec 2013 and was completed in Feb 2014 allowing the start of Magnesium removal.
The Lithium plant commissioning got underway in Oct/Nov 2014 and the first product was coming off the line at the end of the year. 
Then came the ramp up...
 
So where are they up to now - from the quarterly
Five new harvest ponds (17A, 17B, 18A, 18B & 16B) have been completed and are being filled with concentrated brine, replacingpond area that is temporarily unavailable due to salt harvesting activities as discussed earlier. Two new evaporation ponds (15A& 15B) were also completed during the December quarter. Vegetation clearing and construction of two new evaporation pondshas commenced (14C & 20A). A further three harvest ponds, brine reservoir storage pond (TK 1100) and brine transfer ducts arecurrently under construction.7During the quarter construction of a new reactor began at the existing primary liming plant. This reactor will enable the primaryliming plant to process a higher flow rate of brine before the Stage 2 liming plant is built permitting brine stocks to be increasedand facilitating the rapid filling of Stage 2 ponds, as well as a mobile secondary liming plant that would be installed by lateFebruary.Construction of major equipment for the Stage 2 primary liming plant commenced during the quarter and is progressing wellwith key items being awarded to a local companies. The Stage 2 liming plant is expected to be completed in Q3 FY19.

Progress with the liming plant is critical - they can only fill new ponds as fast as they can lime the brine in excess of stage 1 production requirements. The sooner it is ready the better...
Comparing current progress with stage1, H2 CY20 should be ok for the start of commissioning.
Will we see meaningful volumes of production in 2021? That depends on how well the stage 1 lessons have been learnt...