Nothing That Matters

We live in a four dimensional space-time. Three are spatial dimensions and the fourth one is Time. Have you seen time go by. The three spatial dimensions are quite accessible to our physical senses. Although we are sure that Time does exist, but we cannot physically connect with it. Its the unseen dimension.
String theory propounds a universe consisting of 10 or 11 dimensions. Are other 6-7 dimensions also as ephemeral as time. Once we accept that in our 4-dimensional universe one dimension is already ephemeral - its not difficult to come to terms with an idea of higher-dimensional universe. The additional dimensions can be curled up or extended finitely/infinitely.
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I have written about the enigma of time before. Suffice here to highlight that time as a dimension is substantially different from other three dimensions.
Time is always flowing - moving, but the spatial dimension are stationary. Time is only uni-directional, but other dimensions can freely be traversed in either direction.
Still time and spatial dimensions are considered to be an integral whole space-time. Its only we, who try to discern different dimensions to it. For example fixing three mutually perpendicular dimensional axis is just an arbitrary exercise. For space the three dimensions are not distinguishable from others - the three are integrated enough - that we cannot de-integrate or differentiate them. We can substitute one of the spatial dimensions by any one of the rest of two - without changing the equations etc. So should be time. It should not be differentiable from spatial dimensions - we should be able to substitute any spatial dimension for time and vice-versa. But that is not true.
What gives?

It has been long since I wrote. Ironically the last post was - "Updates Keep You Happy". This pause caused by other problems, gave me time to ponder - Am I going nuts on my hypothesis. Sometimes we make castles over wrong foundations and these can come crashing down at the first whiff of introspection. Life is too short and I am at the short end of it at 55. It would be pathetic if after years of study and research it turns out to be a wild goose chase.
I do realize that although the questions that I posit are genuine. The hypothesis is also within realms of possibility. This model building in physics is most fascinating but too conjectural.
I realize that the hypothesis I give is too much coloured with classical-mechanics. So I have decided to look inwards for inspiration and fit the genuine questions into new bottles - rather than in old classical-mechanics bottle.
Hope I do not disappoint my readers.