During the early war years, Nazi leaders were supremely confident of victory. By the end of 1941, the future looked far less certain. Nazi Germany now faced a global war, following the entry of the USA, and major losses in the Soviet Union. In response, the Nazi regime redoubled efforts to increase war production. This also affected the concentration camps. In spring 1942, Himmler placed them under Oswald Pohl’s WVHA (Business Administration Main Office), to harness “every last working hour of every person for our victory”. Pohl duly urged his commandants to exploit prisoners to the limit, causing yet more illness, injury and death.
[…] The camp commander alone is responsible for the employment of the labour available. This employment must be, in the true meaning of the word, exhaustive, in order to obtain the greatest measure of performance.[…] There is no limit to working hours. […] Any circumstances which may result in a shortening of work hours (e.g. meals, roll calls) have therefore to be restricted to the minimum which cannot be condensed anymore.
Source: http://nuremberg.law.harvard.edu, document R-129