I think they are probably facing lot of technical and...

I think they are probably facing lot of technical and infrastructure constraints to start building the ponds early.
Reading the EIA, there are lot of conditions they have to meet before constructing.
From my perspective, if they can get the EIA fully approved by September, things will be pushed back earlier for 3 months. 
All the current assumptions are made based on the worst care scenario, i.e EIA approval by end of 2019.
In addition, they put lot of fat to their estimated so there won't be much surprise down the track.
The progress of the EIA looks very promising. All the Chile government Agencies seem very engaged and provided their feedback proactively.