Ok, I combed through the 2003 Parecon book, which I take to be the most recent.
It appears clear that people can choose their own working hours and intensity:
"In a parecon it is true that people self-consciously decide the
labor/leisure trade off and do so free from compulsion. That is,
in each new planning period each person has two priority
decisions.
"1. How much, overall, do they want to consume?
"2. How much, overall, do they want to work?"
The idea is that if you work harder or longer or whatever, you can consume more. Less work, less consumption.
(Of course, this may be just, but not necessarily compassionate. The authors argue that a decent society will need safety nets too.)
Measuring effort (hours, intensity or whatever) can vary between workplaces.
Tayssir