Or it means they recognize that passion is a finite resource that takes time to replenish.

Works too hard for too long at something you are passionate about is a good way to lose the passion for it you once felt.

So someone who is trying to negotiate less time doesn't necessarily mean they are less passionate about their work; it may just mean that they are mature and self aware enough to realize that they'd like to work at a pace that allows them to sustain that passion over the long term.