Toronto Hydro has been doing work at edge of the site for about 2 weeks, they seem to be installing an underground concrete space (for transformer ?) under the street at the NE corner, and trenching West under Cordova Ave.
The March update says they received their excavation permit, so I expect that to get rolling soon.
It appears as though the show will get started soon. They've finally fully closed off pedestrian access to the parking lot. I'll post more when I see more activity.
These often take place once the site has been cleared, though it could still come sooner. I would still expect something official to happen fairly soon.