If when viewing the chart army for a replay, clicking on a Unit/Tech/Building could move the time-cursor on the graph to the moment the first unit/tech/building of this type was created, that would be great for watching timings !
E.G: If I click on Stimpack, I can immediately see what was my army composition and the one of my opponent when the stim upgrade just finished.
Same if I see him going cloaked banshee, I could click on my raven/turret, to see exactly from when I was able to correctly defend cloaked units.