We're all getting crossed wires about our definition of time here.
There are two types of time.
Absolute Time. This is whats shown and measured by external zeitgebers and is the dimension.
Personal time. This is time how we perceive it as measured by our internal body clock (set at a 25 hour standard) which we can make faster or slower by our actions. This is not a dimension so much as our reaction to time.
As for all this messing with time business it really depends on your philosophical views though I believe that any disruptions in the time line won't affect me as I am here as living testament. You can't argue against that by saying it may happen in the future as its already happened in the past and it made me so the universe as we perceive it will be unaffected. What is a possibility is that a parallel dimension appears containing what happened when the time line was messed in (Like on BTTF) this is unknown and again could only possibly affect us in the future because it has already happened.
I'm no ace at physics, I got a B for GCSE, didn't take A level and cringes whenever someone mentions 'String theory' (although I am to believe its something to do with there being 22 odd dimensions) but thats my understanding of time
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