(SP Population module required for the above two options) The negative number will subtract leave time from what the game already provides I don't really think anyone gets more than 10 paid days off per pregnancy. NRaas > SP > Town Options > Pregnancy:Maternity Leave > (default is +1, change this to something like -10).
This will prevent SP from adding additional leave days to what the base game already provides. NRaas > SP > General Options > Options:Pregnancy > Maternity Leave > False So what you would want is, on City Hall or an in-game computer, What SP does is apply additional days on top of (not instead of) what the game provides.
The amount will depend on their job, job level, and some other factors. The way this works is that the game already grants parental leave to female sims. I have to admit that the settings for parental leave are not the most intuitive to work through.