I don't know if this is enough, but if you right click -> inspect element on the timestamp, you'll see something that looks like:

<span class="duration" data-starttime="2018-03-22T21:06:46Z" data-endtime="2018-03-22T21:13:11Z" title="Started:  2018-03-22 2:06 PM (PDT)
Ended: 2018-03-22 2:13 PM (PDT)">
          ( 6 mins 24 secs )</span>

Note the data-starttime and data-endtime are the UTC timestamp of when this step started and stopped.  Is this sufficient?

I really want to avoid adding in seconds to the timestamp because the information density becomes higher.

(please ALWAYS include links, it makes it easier to triage bugs)

hinoka, can we display seconds in the tooltip? it wouldn't increase the information density overall

We definitely can, i'm on the fence as to whether or not we want to.

I didn't include link since it affects any build, e.g. https://luci-milo.appspot.com/p/v8/builders/luci.v8.ci/V8%20Linux64%20-%20builder/443.

Re using inspector from #1: this is a good workaround, but not very user friendly or discoverable.

I also think adding seconds to the tooltip wouldn't increase density, so it's probably a good compromise.

CL: https://crrev.com/c/1026001. Preview here:
 - https://2970-2613891-tainted-sergiyb-2-dot-luci-milo-dev.appspot.com/p/v8/g/main/console
 - https://2970-2613891-tainted-sergiyb-2-dot-luci-milo-dev.appspot.com/buildbot/client.v8/V8%20Linux
 - https://2970-2613891-tainted-sergiyb-2-dot-luci-milo-dev.appspot.com/buildbot/client.v8/V8%20Linux/24448

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/luci/luci-go.git/+/95f4cbc14ff6a959f90212b30ea47df4e07dd7ff

commit 95f4cbc14ff6a959f90212b30ea47df4e07dd7ff
Author: Sergiy Byelozyorov <sergiyb@chromium.org>
Date: Thu Apr 26 00:22:48 2018

Show seconds in timestamps shown in tooltip

R=hinoka@chromium.org

Bug:  826430 
Change-Id: Iff15bf724067bf57aaf521ceb3f8285e47d41224
Reviewed-on: https://chromium-review.googlesource.com/1026001
Reviewed-by: Ryan Tseng <hinoka@chromium.org>
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>

[modify] https://crrev.com/95f4cbc14ff6a959f90212b30ea47df4e07dd7ff/milo/frontend/appengine/static/common/js/time.js

Update: this above change does not add seconds to tooltips on step duration. I'll prep another CL and then deploy both to prod.

CL: https://crrev.com/c/1030690

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/luci/luci-go.git/+/c1f43613bbb1dc929d304123e849b9134b0c6e48

commit c1f43613bbb1dc929d304123e849b9134b0c6e48
Author: Sergiy Byelozyorov <sergiyb@chromium.org>
Date: Thu Apr 26 20:11:50 2018

Also add seconds in tooltips for step duration

R=hinoka@chromium.org

Bug:  826430 
Change-Id: I7d2bea1de25373bc857d37f0b7ad1e82b0f331c2
Reviewed-on: https://chromium-review.googlesource.com/1030690
Reviewed-by: Ryan Tseng <hinoka@chromium.org>
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>

[modify] https://crrev.com/c1f43613bbb1dc929d304123e849b9134b0c6e48/milo/frontend/appengine/static/common/js/time.js

All changes deployed to prod.