I'm letting timechart choose the proper bucket size, but I want that size to be displayed somewhere. I'd like to be able to have the chosen bucketsize appear in a legend so that when you look at a graph you can understand the Y scale.
See this run anywhere sample. You should see the span in duration format (1h=01:00:00, 1d=1+00:00:00)
index=_internal | timechart count | delta _time as span | eval span="span=".tostring(span,"duration") | eval {span}=0 | fields - span