SSHQ us starting to go vertical now.
But I'd say Winthrop Center starts going vertical sometime in early 2021. (February?).
Then I'd say SST goes vertical sometime in late 2022.
Winthrop Square is top-down construction - should go up before February. What you see going up now is going to continue climbing pretty consistently/quickly, provided everything goes smoothly. The first few floors are a little different (with the "great hall"/lobby and the differing entrance elevations), but after that, there's no reason it will take a while to get climbing.