AC does have a desk at the transit centre but I find it is no always "manned". I suspect they put someone there within two hours of their departures, but based on one experience, the agent generally leaves 45-minutes or so prior to flight departure of the last flight out in the evening. Given there is a cluster of departures around 1pm, this desk is likely serviced in advance of the 9am departure, then again for the early afternoon ones.