you left the reservation, when you started in on 'time'. here is why:
time is, in whole, a construct of the human mind. our mind only uses time to make sense of our experiences.
time really has nothing to do with epistemology.
and, no, time is not divided into discrete 'steps'. that is a famous paradox (based on a fallacy):
Zeno's Paradox of the Arrow
as for light.... it just is. no entity set the limit. it just is what it is.