  We introduce a parabolic version of the so-called John-Nirenberg space that
is a generalization of functions of parabolic bounded mean oscillation.
Parabolic John-Nirenberg inequalities, which give weak type estimates for the
oscillation of a function, are shown in the setting of the parabolic geometry
with a time lag. Our arguments are based on a parabolic Calder\'{o}n-Zygmund
decomposition and a good lambda estimate. Chaining arguments are applied to
change the time lag in the parabolic John-Nirenberg inequality.
