  MoSe2-WSe2 heterostructures host strongly bound interlayer excitons (IXs)
which exhibit bright photoluminescence (PL) when the twist-angle is near
0{\deg} or 60{\deg}. Over the past several years, there have been numerous
reports on the optical response of these heterostructures but no unifying model
to understand the dynamics of IXs and their temperature dependence. Here, we
perform a comprehensive study of the temperature, excitation power, and
time-dependent PL of IXs. We observe a significant decrease in PL intensity
above a transition temperature that we attribute to a transition from localized
to delocalized IXs. Astoundingly, we find a simple inverse relationship between
the IX PL energy and the transition temperature, which exhibits opposite power
dependent behaviors for near 0{\deg} and 60{\deg} samples. We conclude that
this temperature dependence is a result of IX-IX exchange interactions, whose
effect is suppressed by the moir\'e potential trapping IXs at low temperature.
