When you live in the present, time is linear. By that I mean that you are only processing the sights, sounds, smells of that second, then the next, but not processing each second simultaneously. You are expansive, experiencing many different facets of that second simultaneously and taking them all in. Time is distinct; it is not aggregate. For example, if you look at a clock, you do not experience that the hands are in all possible locations within any single second; instead, you experience that the hands of the clock are each in a single specific location within each given second.)
When you live in the future, time is also likely to behave mainly in linear fashion. It is more likely that possibilities are extrapolated based on logical & rational factors rather than arising randomly as extrapolated collections of random factors. For example, if you think about having children you also must think about how you are get children. Will you get married, have a one-night stand, clone yourself, etc.? Because the future exists based on logical assumptions (unless you are looking at an emotionally-driven future, such as a fear-driven future such as a post-apocalypse that may be randomly generated by emotional fears, but really this is getting too deep into this theory for this post and such emotion will still likely generate one main possible future which is a single point in time which creates linear time) and logic builds upon itself, this process is mainly linear. It is not linear in the sense that you can move forward & backward through the process. For example, you can think about getting a college degree, and then move backwards to think about how you get the degree (but this is all still living in the future) or you can then move forward along a linear time-line and think about what kind of job you will get after college.) When living in the future, time is also distinct and not aggregate. You can think at any one point in the future, and move forwards & backwards through that point, but you are usually just at that one point. (I have Ne, so I understand that some of us live at many points in the future simultaneously, so I apologize for this over-simplification and may expand upon this part of the theory in the future.)
When you live in the past, time is experienced in a non-linear fashion. All of your memories exist simultaneously in your brain. The only limit to this non-linear nature of time when you live in the past, is your capacity for holding ideas & emotions in your head simultaneously. For example, when someone bullies you and this causes you to recall past times when you were bullied, you recall the collected sum of all the times you've been bullied simultaneously and this creates an aggregate emotion. You do not experience each single bullying incident in linear order as separate events; instead this focuses the intensity of your emotion into a bullying category that is then triggered during a bullying event. This non-linear experience of time creates a greater emotional intensity than that which can be created through a linear experience of time. So, you see, my INFP nihilism arises mainly because when something bad happens, it is not a single thing that happens, but instead that one thing plus all the other bad things in the past that are tied to it as far back as my memory came into existence, and they all happen simultaneously. Given the weight of that aggregate experience, who wouldn't be nihilistic?