Before, the X-axis labels would be placed in nice even positions, but
with whatever odd time corresponded to that. That made it harder than
necessary to read the graph and approximate when things happened.
Instead, round the interval down to nearest power of ten ... and if
suitable, scale that up with a factor of 2 or 5. That will (with the
necessary handling of how seconds/minutes/hours relate) make sure that
the time labels are nice with a minimal amount of non-zero digits. That
makes it easy to do math and interpolate when reading the graph.
The number of labels will change between something like 4 and 10 -
before it was always something like 7. That is fine, as long as it helps
the readability.
The total length is no longer the right-most label, but the length can
be found in the top-right corner.
