I’m pretty sure that this will happen in later stages of construction. Certainly during TYSSE there were photos of TTC work vehicles in the tunnels well before commissioning.Sorry but just reading what you wrote and interpreting it differently, wonder if the rails could become a means for construction. No more concrete trucks and dump trucks clogging area roads during station construction. Use the rails to bring everything in and out. Materials, workers even. Build stations from the inside out. Maybe build the stations in consecutive order so we don't have a dozen construction sites lasting a decade. Have the rails first, and let's use them to our advantage.
I’m not sure the construction forces get much of a logistical benefit from the tunnels - by the time the tracks are laid, the really heavy material handling has already happened, and the big mechanical things (escalators, HVAC, etc) need to come in vertically from above, would not fit thru the tunnels. So long as the cranes have to be there anyways, might as well use them.
For the moment, even without rails in place, having the floor poured at least gives them a finished “floor” work surface.