The uncertainty principle establishes that you cannot know momentum and position at the same instant of time. It follows then that the relationship between the two quantities will become more 'disturbed' when you try to improve the accuracy of either, separate measurement.
A smaller error margin in one, will result in a bigger error margin in the other, I think?
If you attempt to go smaller than Planck values then yes, the theory predicts a black hole or 'quantum foam.'
Hawking radiation suggests time does not stand still inside a black hole and that over an immensity of time, a black hole will evaporate.
Your statement does not prove that spacetime is not quantised to the same level that current efforts do not prove that it is. We just don't know yet but I would currently move towards the 'yes spacetime is quantised' side, based on what science has found so far. So, I still hold, in general, that time (or spacetime) is 'real.'
For me the more pressing questions, relate to:
if spacetime is the 'real' state then distance and time are 'not separate' quantities, so, expansion of space, is the notional 'clock' ticking. The current expansion rate is accelerating, This suggests that the 'rate of time' must also be accelerating but this further suggests a 'universal' reference frame for time as well as the more localised, relative, reference frames, within which the phenomena of 'time dilation', occurs. The divisor in the time dilation equation can tend towards zero, which suggests that if you could travel at light speed (within space as currently understood) then you cannot age and you could theoretically outlive the universe you are traveling in!!!
Another mind f### is that in your own reference frame you would still only live your own lifespan.
This reference frame would be effectively 'outside of the universe's reference frame.'
This is based on the premise that Is it correct to say that in the 'Universal reference frame', a photon, traveling at light speed, does not experience spacetime at all? It only enters spacetime when it slows down due to interaction/change in property/pair production etc.
I do have some fun playing with this, with more (perhaps philosophical) thoughts like; 'so, is this like the state dead and the state alive?'
is a photon effectively dead when it does not experience spacetime? does it become alive when it enters spacetime? How does this relate to the human experience? Probably nonsense, but it stops my head from exploding when I try to approach anything near to an understanding of this stuff.