Ability to measure custom spans/metrics

It would be useful if one could use the flashlight api during e2e tests (or some other way) to measure custom spans like TTID (time to initial display), TTFD (time to full display) of screens or tabs or just general operations that span multiple renders like a "how long does it take for dialog x to show up when I click button y". These would fit perfectly with flashlights repeated execution model to normalize the measures.

I"m not sure if Maestro allows timing such things (unfortunately), but maybe other e2e frameworks could (like Detox). An example user flow could be:

- Open app
- Goto tab A, wait for content to load
- Goto tab B, wait for content to load

In this flow we could have 4 metrics, 2 for each tab:
- "navigation time" or TTID: starting the span when the test touches the tab bar button for the respective tab, and ends when the test sees the first rendered frame/content on the respective tab content screen
- TTFD: same start as TTID, but ends when the test sees some final content visible in the respective tab content

Would this be possible/fit into the scope of flashlight?