question on (delta(t) ~ delta(x)^2)??

hi evrybody
In the article “Choice of units in lattice Boltzmann simulations” and the paper “Asymptotic analysis of the lattice Boltzmann equation” for incompressible flows,it is shown that delta(t)=O(delta(x)^2)
question: what are the dimension of delta(t) and delta(x)?

delta_x could be in [m], [mm], [micrometer] …
delta_t could be in [seconds],[miliseconds]…

delta(x)(lbm_length)=(physical_length)
delta(t)
(lbm_time)=(physical_time)