Define, document, verify what time is used for various reconstructed quantities

[wdconinc]

Is your feature request related to a problem? Please describe.
In some reconstructed quantities the time is the earliest hit. In other reconstructed quantities it is the first hit in the collection. In yet other reconstructed quantities it could be assumed to be the highest energy hit.

Describe the solution you'd like
The edm4eic data model is silent on what the time should be. We should define this better, document it in edm4eic, and verify it here.

Additional context
#1224 (comment)

[veprbl]

This was touched upon by @kkauder at the background session the other day.

My take would be that we can't start implementing this before we have semi-realistic background timings and some info from electronics people on how digitization should work.