 Inflation condition for a homogeneous massive scalar

In flat general relativity with no separate cosmological constant, a canonical massive scalar has $\rho +3P=2{\dot{\varphi }}^2-m^2{\varphi }^2$. Accelerated expansion therefore requires ${\dot{\varphi }}^2<m^2{\varphi }^2/2$. Initial potential dominance is an instantaneous condition and does not alone fix the duration.