Aye just tested Dr.Boom and it looks good. I even had a mage join in at 40% or something and it picked him up really nicely.
I'm posting graphs of the 2 of us if they will be of any use to you. The fight lasted for 12 minutes and 15 seconds.
This is a graph of me. It's really nice to see my dps drop at the same time i needed to drain life (my healing picks up). And my peak at over 1200 DPS at the end was a back to back crit. The visual representation can really help remember certain events.
This is the mages DPS chart. He joined late, died once

and then rezzed and continued to help since he needed the quest. He also stopped dpsing a few times (OOM). All of which can be seen on the graph.
All in all I'm very pleased with the representation of the lengthier fights so far.
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Regarding the X-label:
- I can foresee some problems in lengthy fights like this, since it'll be hard to see events that took 10 to 20 secs due to the scale having to incorporate all 12 mins. Now the first thing that comes to mind is for the user to choose a certain segment to view more carefully or to be able to change scale of the x-axis, but in the latter case you'd need a way to scroll the graph horizontally then, which might be a problem I guess.
As for the label on the x-axis I suggest for the default to be seconds of the fight divided into the 25 sec chunks you use to measure data.
This is all of the top of my head right now so I could be suggesting something too extreme, since I've never coded in LUA before.
And ofc, great job so far!