I have not been able to find any substantial literature in psychology on this topic. This is surprising, but it could be that I still haven't found the right phrases to search with; I'm not a psychologist! But from what I have gleaned intentional thinking is what you do when you actively decide to think about a topic, situation, or whatever seems pressing. You intend to think about something and generally it proceeds in inner dialogue using language. Reactive thinking, on the other hand, is when your mind is trying to apprehend sensory inputs to understand what you are experiencing, as when you are reading a book, for example. Both of these are distinguished from imagination or day dreaming in which the brain is not really actively pursuing a specific thought, at least not from conscious pursuit. The brain is active in day dreaming, but pursuing some unconscious objective, like imagining sexual pleasures (or any other pleasures), which I have read occupies a substantial amount of adult male thinking!
And that brings up the relative amounts of time spent in intentional versus reactive (versus day dreaming) thinking. I haven't found any studies that ask such a question but I have some, possibly testable, hypotheses regarding the norms. From casual observations (and querring) of many friends, acquaintences, and associates I am led to suspect that far more time is spent in reactive thinking than in intentional thinking. The former is necessary for social interactions; you have to be thinking about what other people are saying and doing. Your thoughts react to their thoughts and actions. This doesn't mean you aren't actively and consciously thinking. It just means that your thoughts are guided by an immediate environmental stimulus. Intelligence, creativity and judgment are still very much brought to bear in these situations.
In contrast intentional thinking is most often done alone and in one's head. Or it may be done in a social situation where you have abstracted yourself from the social exchange to take a 'meta' view of what is transpiring. You aren't thinking about how to respond to your friends, say. You are thinking about the nature of the exchange between others and seeking some deeper meaning. But these tend to be fleeting moments and soon pass as you reengage with the conversation/activity.
The key question related to sapience has to do with how much time one spends in intentional thinking and the scope of that thinking. Do you often think about the long-range future of society? [Many of the longer term readers of this blog will likely answer yes!] Most people, I suspect, spend very little time in intentional thinking about anything more than what they want to get at the store. Thinking a lot about what is good for the earth, for humanity in the future isn't on most people's regular agenda.
Sapient judgment is used to choose what and how much to think about stuff.
Note that reactive thinking, even day dreaming, takes intelligence. Indeed much of our human intelligence is dedicated to social interactions and solving the complex web of social situations. As a younger man I tried hard to be interested in sports statistics and even managed to learn a few stats about the San Diego Padres that I could use in the seemingly casual conversations with other guys (men and women now counting as guys). These conversations are, of course, anything but happenstance. They are part of the bonding process that members of our technological society engage in to strengthen our sense of us. It takes a lot of intelligence to study and remember key statistics and to know how to use them in conversations meant to show your sharing of accute interest in these (manly) activities. A lot of judgment is needed to decide which teams to follow, which statistics are important for the purpose of demonstrating knowledge (and impressing others). But how important are these machinations of mind for the world? I just never could get into it. I don't play golf either. For much the same reason. It isn't that I am anti-social. Quite the opposite. I'm always trying to organize social gettogethers at work. But I would prefer to talk about things which seem particularly important right now.