Thanks, WB DT.  April it is, then... unless it changes again.  I don't know when construction can begin out at Thacker Pass as far as the weather goes but the link below may give some insight in regards to climate conditions at nearby Oravada, Nevada:

Climate Orovada - Nevada and Weather averages Orovada (usclimatedata.com)

Looks like April might be the earliest?  As far as Reno goes, I have seen it snow here in June, so it is hard to predict when the cold leaves, but miners are a hardy lot and I don't think a little cold weather would stop them.  Snow and ice, however might make it more difficult.  My guess would be April would be accomodating for construction out at Thacker Pass.

Okiedo