If my source's info is accurate; and I don't doubt them at all; but they are as at the mercy as the rest of us to Mx, or the consortium not achieving what they were supposed to by date 'x'.......The TTC would have sufficient lead time to begin to operate sometime in Q2.
As
@Steve Munro has pointed out above, there is a lead time from the moment the TTC is told 'GO' to being able to have the line staffed up, the minimum lead time is one Board Period, (sign-up for routes by operators), which varies in length throughout the year, but would be ~6-8 weeks on average, but the lead time is actually a bit longer, as someone has to order the new schedule into effect and create the sign-up ups for those schedules, which won't be changed the day or even the week before they are supposed to go up.
To bring this back together, I think a Q2 date from mid-April through end of June should be viable if other targets are hit as they should be.
But the latter remains to be seen.
Ramping up service in the summer would seem odd to me; as the TTC has to deal with vacations like any employer, and generally cuts back service going into summer. But we shall see.