This seems odd because there clearly time dilation effects between two observers even when they are not accelerating but merely have a large difference in relative constant speed.
You seem to be saying that there has to be constant acceleration between observers for this effect to take place.
My apologies I really didn’t explain myself very well at all. That was quite confusing. This formula represents a trajectory in spacetime with respect to some frame of reference of an observer. As with any trajectory it has space and time components.
The x, y, z deltas are your displacement through space in those dimensions relative to some frame of reference (of an observer, presumably) and t is the time component. If the space deltas are all zero then you are at rest relative to that inertial frame. You are not accelerating or moving and your motion through the time dimension in unit time, according to this formula, is C. This is odd because C is normally thought of as a motion through space, but in this case your not moving through space (in the reference frame).
You seem to be saying that there has to be constant acceleration between observers for this effect to take place.