Alternative point of view is that each system has its own individual time measured by the number of events. For example, time in human life can be measured by the number of decisions made. A person who lives passively, and avoids making decisions, remains a child psychologically even if he is biologically an adult. We can apply the concept of biological time to the development of poikilothermous organisms. The progress in organism's development can be viewed as a biological clock that measures physiological time.
Physiological time goes fast when it is warm and slow when it is cold.
Then, development rate can be defined as advance of physiological time per unit of calendar time. To determine the duration of development we will accumulate development rates rather than effective temperatures. There is no mechanical watch that measures physiological time. Also there are no hour and minute hands inside an organism. However, in some cases it is possible to find indicators of physiological time, e.g., concentration of hormones and metabolites, CO 2 emission rate, etc.