In my opinion - yes. That’s what I use and recommend to always use. (but opinions vary on this forum)

For as long as you’re not inserting the timestamps manually (e.g. insert_all), but let ecto handle them you can basically switch them out at any time. Ecto does default to NaiveDateTime.utc_now(), so it’s going to be a utc datetime no matter what and on the db side there’s no difference between an :naive_datetime and :utc_datetime field.

How can I convert “inserted_at” from naive to utc so that I can use it in DateTime.diff(…) ?

Either use DateTime.from_naive!(a.inserted_at, "Etc/UTC") or setup your schemas to use :utc_datetime.

this has been on this forum quite a few times already (search for utc_datetime). In short: when you use Ecto only, this should not matter as it enforces client’s protocol to be in UTC time zone. However, it makes difference if you load scripts or perform queries using psql or other external tools, that can have different time zone settings.