A qulified person, usually on the de-icing team, will conduct a check post spraying to ensure the aircraft is clear of contamination. Different aircraft manufacturers and operators have slightly different drills and checks to complete post de/anti-icing. This can include delaying take-off flap selection till the holdng point for the departure runway and a full and free control check. Should snow or other freezing contamination be falling after the treatment process, the commander needs to asses whether the hold over time is still applicable and then check by visual means, if the wings are clear of contamination. If there is doubt or the checks can not verify that the aircraft is definatly fit to depart......the process starts all over again. Different temps, weather and fluid types and concentrations give different HOLD OVER TIMES that change as the conditions change. they are only a guide and not definate. If the Aircraft has been parked over night and only requires de-icing, this can be done no longer than 60 mins before departure( 45 mins in my company) and as such the aircraft may have been sprayed befor the crew arrive. It is the commanders job to ensure the treatment has worked, and order any other treatment as required.