preons have been postulated but no experimental evidence was ever found. It is somewhat of an outmoded concept as it they have not been included in the Standard Model.
If by some remote chance you are interested in particle physics but never visited http://particleadventure.org/
I suggest you check it out.
Quarks are hardly particles in there own right as they have never been observed individually and their existence is only possible when together they are composing a larger hadron (like a proton or something weirder).
Time is trickier. Many physicist believe that aspects of quantum mechanics suggests that time and space are discrete quantities with a smallest possible unit known a plank unit. The problem is that this is at odds with relativity.
Relativity say that measurements of space and time change depending on your reference frame. How could there be a smallest measurable unit when your measurements change depending on your reference frame?