Time needed for Hydrogen Cyanide pellets 'Zyklon B' to change into gas and take effect.
Description	Temperature of room		Hours needed to take effect	Effects of temperature on Cyanide pellets
	degrees C.	degrees F.
Temperature to prevent condensation	31	90	3	Minimum air temperature that cyanide gas is released from pellets in a relatively short time period.
Boiling point of Zyklon B	25.7	78.3	6	Minimum temperature gas starts to be effectively released.
Estimated range of temperatures for the floor of below ground level morgue	20	68	14	Pellets change to gas very slowly
	15	59	18
	10	50	24
	5	40	32

Testimony by 'witnessess' at post-war trials claimed that after Zyklon B pellets were dropped through roof vents, the time to kill everyone was 3 minutes in summer and 15 minutes in winter.

Based on figures in the above table, it actually would have taken many hours for Zyklon B pellets to slowly release enough cyanide gas to begin to affect people's breathing.

References:

Summary of information found in the following publications:
1. "Hydrogen Cyanide - Manual for Safe Use" by Dupont Chemical - page 39
2. "Nuremberg International Tribunal - Document #NI-9912"
"Directives for the use of Prussic acid (Zyklon) for the destruction of vermin (disinfestation)."