The time ladder is the stepped line running along the bottom of a value stream map. Its upper steps are value-add time (the process time of each step); its lower steps are wait time (inventory between steps, converted to time via Little's Law).
The totals on the right
At the right end, the ladder totals both clocks and reports Process Cycle Efficiency. In most unimproved streams, PCE lands in the single digits — a sign that product spends the vast majority of its life waiting, not being worked on.
What to do with it
Target the tallest wait steps first: they're the biggest inventory buffers, and draining them shortens lead time far more than shaving seconds off a process. That's the whole point of mapping — it tells you where to aim.