// 1. if all containers finished, use the latest time
// 2. if the pod has Ready=False condition, use the last transition time
// 3. if the pod has been deleted, use the `deletionTimestamp - grace_period` to estimate the moment of deletion
// 4. fallback to pod's creation time
//
// Pods owned by Kubelet are marked with Ready=False condition when
// transitioning to terminal phase, thus being handled by (1.) or (2.).