I came arrived at YYZ yesterday at about 12:30pm, and was anticipating using their new OSS setup for the first time. Fortunately it was easy to observe the crowd as I approached the top of the escalators. There was a long line stretching back along the corridor from the E gates, and there were two only CBSA officers processing them. Arriving passengers use kiosks before reaching the officers, but there is no sign of Nexus yet. So I headed downstairs, used Nexus there, and was able to move quickly out of the customs area and through security on level 3 to get to the domestic side.