Almost all small dianions known from condensed phases are unstable with respect to electron loss in the gas phase. Here we study the electron autodetachment lifetimes of CN22-, C-4(2-), and CO32- employing the complex absorbing potential method as well as a new variant of the stabilization technique. The investigated temporary species show rare-gas-like closed-shell electronic ground states, and we discuss conceptional and technical differences between closed-shell resonances and typical "temporary anions" associated with electron scattering from closed-shell targets. The computed lifetimes set a lower limit for the time scales of experiments intended to observe the free dianionic systems, and the trends of the lifetimes can be understood in terms of the ideas established to rationalize the electronic stability of bound dianions. Finally, we discuss the question of which properties of metastable dianions can be extracted from bound state calculations, effectively ignoring the temporary character of the examined system.