Yes, there is indeed a concept of a very thin line between the past and the future. Our perception of time is such that events that have already occurred are considered part of the past, while events yet to happen are part of the future. The present moment is often seen as the dividing line between these two.
As you mentioned, even a minuscule increment of time, like a fraction of a second, can be considered part of the past as soon as it has elapsed. The passage of time continuously moves events from the future to the present and then into the past. This concept reflects the linear nature of time as experienced by us.
However, it's important to note that this concept of a thin line between the past and the future is subjective and based on our human perception of time. From a more abstract or scientific perspective, time is a continuous and interconnected dimension, and the distinction between past, present, and future may not be as sharply defined as we perceive it.
The study of time and its philosophical and scientific implications is a complex field. Various theories and interpretations exist, such as the block universe theory, which suggests that all events in time exist simultaneously, and our experience of time moving forward is merely an illusion. Nevertheless, in our day-to-day lives, we generally operate with the understanding that events progress from the future to the present and then become part of the past.