I know there's a plug-in for this, but page load speed should be a default metric. This should be available out of the box without custom code or requiring use of a custom event. There are enough mysteries when solving SEO riddles!
The plug basically buckets the time into time bands. This is also useful. With some extra work, you can set the time to a metric and get the average page load time for a page or group or pages. I assume the latter is what is being requeste here.
I'm using the plug-in. Not seeing a ton of value yet. Anyone have relevant examples where they get some insight? FWIW - I implemented it as specified so I have all 10+ grains of timing. That also seems like overkill to me and this is coming from a devOps former life.
I ended up adding a few extra events to it to measure total time to domInteractive/contentloaded/complete. This seemed a bit more useful than all the granular stuff for most things.