Anyone in your Tribe with lower than 100 Will who also has the Spineless Trait in their personality, seemingly will be the ones to complain about your normal workhours (default 12).
So you can calculate who will quickest complain about workhours even at normal/default workhours.
What I have experimented on is to “trick” the spineless by reducing to 8 or even 4 when they feel overworked, for then to move back up to 12 as soon as they calm down.
This can take a month or so as it seems they take equal amount of time to become happy again as they did to become unhappy. My experience is that as long as the spinless dont reach “exploited”, they will not leave the tribe, so a bit of jo-jo-ing of the workhours should keep them from leaving.
This is not written in stone so keep an eye on your spineless people.
I will only keep the spineless members around till they (if females) have had a child and it has become an individual.
Asap the spinelss women/woman is without a child or toddler I put workhours to 12 permanently unless we move towards famine, where I will add it to 18 for a 1 month burst in food income after migration.
If there are only spinelss males I do not touch the workhours. (Fears being called out for discrimination) 
If any of you others are experimenting around also, let me know how you guys are doing please, share hints and tipes and definitely do share your “A-HA” moments 