Automatic shutdown of iPhone on timer or at a specific time

Instead of powering it off completely, "Airplane Mode" might accomplish what you want. No RF and reduced battery consumption, and has the advantage that you can script it to turn Airplane Mode off automatically sometime later. Any wake-up alarms are still possible.

If you leave it plugged into a charger then you don't worry about battery power.

In the version of Shortcuts that I have, there is an action to "Turn Airplane Mode On" or "Turn Airplane Mode Off" or "Toggle Airplane Mode". I say "my version" because I downloaded the "Actions" utility app by Sindre Sorhus in the App Store. It's free.

It does not do anything by itself and has no user interface. All it does is make dozens of additional actions available to the Shortcuts app. I don't know if "Turn Airplane Mode ON/OFF" is one of them or it it's one of the default set.

[later...]

Oh. Maybe it is part of the default set of Actions.

See this thread: Shortcuts: Automating Airplane Mode - Apple Community

Instead of "When / Do Not Disturb is On" turn Airplane Mode ON right away, and then add something like When / Timer Ends", DO [some Actions that turn Airplane Mode off 8 hours later].

Maybe there's also a way for it to wait for the end of an episode, and then turn Airplane Mode ON, if you need to stream it. If not (any way to detect the end of an episode), then start a time delay to turn Airplane Mode ON just before you start the podcast episode.

FWIW, As a technician who had spent the last 17 years (before retirement) working in a facility with ten shortwave transmitters ranging from 100 kW to 250 kW of RF power in operation most of the day, I'd say you do not have to worry about the amount of non-ionizing radiation coming from your phone.