From the fact that it has already killed some admirals, had taken posession of Ariam and the way it acts in "Project Daedalus", i would assume that it is already sentient for some time...
Well, future-Control took over Airiam, which is when she started sending data back to 31 headquarters, and apparently around the time it killed the admirals (they may have already been dead when they were holoconferencing with Leland and Georgiou last week; it's hard to tell how much time passes between episodes) and stopped taking Cornwell's calls. It looks like future-Control hijacked its past self using Airiam to bootstrap-paradox its own inception.