As for the simultaneity of two or more events, naked-eye observers placed at arbitrary (non-equidistant) locations would typically come to different conclusions, due to the finiteness of the speed of light. This suggests that inertial frame wide simultaneity is not a direct experience but a mere definition, based on an agreed way of measurement. Similar is true for coordinate time and distance, since they both build on the concept of simultaneity. (Already in the case of duration, two co-located observers need to use a clock in order to avoid ambiguity.)
It does not harm to imagine that the above concepts describe a directly intangible "objective reality" in an inertial frame, but as a matter of fact they are essentially just tools that help us in calculating answers to questions about our (more) direct experiences. Later we'll see that the most important question to answer is this: between two events that happen directly to an observer, how much time elapses according to the observer's own clock?