  Compact planetary systems with more than two planets can undergo orbital
crossings from planet-planet perturbations. The time which the system remains
stable without orbital crossings has an exponential dependence on the initial
orbital separations in units of mutual Hill radii. However when a multi-planet
system has period ratios near mean-motion resonances, its stability time
differs from the time determined by planet separation. This difference can be
up to an order of magnitude when systems are set up with chains of equal period
ratios. We use numerical simulations to describe the stability time
relationship in non-resonant systems with equal separations but non-equal
masses which breaks the chains of equal period ratios. We find a deviation of
30 per cent in the masses of Earth-mass planets creates a large enough
deviation in the period ratios where the average stability time of a given
spacing can be predicted by the stability time relationship. The mass deviation
where structure from equal period ratios is erased increases with planet mass
but does not depend on planet multiplicity. With a large enough mass deviation,
the distribution of stability time at a given spacing is much wider than in
equal-mass systems where the distribution narrows due to period
commensurabilities. We find the stability time distribution is heteroscedastic
with spacing -- the deviation in stability time for a given spacing increases
with said spacing.
