[kang]

Its not that simple. Time it seems IS the first (0th?) dimension. A point is space denotes existence in time of the object & observation by the subject. In other words, rate of change of existence is observed as time. Rate of change of a point is observed as a line. A moving point accepts line as its track, moving interval accepts square as its track and moving square accepts cube as its track. 2-eyed observer has 3D vision & 1-eyed observer as 2D vision (try touching your fingers with one-eyes closed exercise) has some role about role of observation as well.

Further, dimensions being relative vs absolute makes more sense. In absolute sense, time is its own dimension T & point line cube are L, L^2 & L^3. A 3D object, a cube, has 2D object, plane, as its boundary & 1D object, lines, as its dimensional denotion. A square has 1D object as its boundary & n-2=0D objects, points, as its dimensions, relatively speaking. This is important because of the number of eyes? So basically, those 2D hypothetical characters in your physics are 1-eyed creatures, lol.