The average time for cremating a corpse is around 2.5 hours in the new cremating ovens for average adult corpse size.
As you know every day has 24 hours. (duh)
Wich means that 24/2.5 = 9.6 corpses per day for 1 oven, and it has to be a non-stop cremation.
According to the initial number "muh" 6000000, this had to happen withing 6 years (being generous here), 1939-1945.
This means 1000000 per year. Meaning 1000000 per 365 days, that translates to 2740 corpses per day (give or take).
There were 8 supposed death camps ran by the National Socialists. That means 2740 corpses needed to be cremated within all the 8 camps per day.
That equals to 342 (give or take) corpses per camp per day.
If 1 oven (of the new ones) can cremate 10 corpses (again had to be non-stop), that means they had to have at least 35 ovens per camp.
No plans for any of the camps show that amount of ovens.
No cremation oven runs non-stop or can run non-stop.
Obvious this is taking into consideration that all body masses were the same, which they were not