Phoenix LiveView - Form Component Auto-Populate Input Fields

I have a Phoenix Liveview Form Component with multiple input fields. When a user enters an event :duration (integer) along with the event :open_at_date (“2021-12-13”) and open_at_time (“13:00:00”), I calculate the subsequent event date/time fields and put each change on the changeset. Resulting in:

changes: %{
    cutoff_at: #DateTime<2021-12-14 16:30:00-05:00 EST America/New_York>,
    description: "some event description",
    duration: 5,
    end_at: #DateTime<2021-12-17 16:30:00-05:00 EST America/New_York>,
    name: "some event name",
    open_at: ~U[2021-12-09 13:00:00Z], (I then convert to --> open_at: #DateTime<2021-12-13 18:00:00-05:00 EST America/New_York>,)
    open_at_date: "2021-12-09",
    open_at_time: "13:00:00",
    rules_list: "",
    start_at: #DateTime<2021-12-15 09:29:00-05:00 EST America/New_York>,
    uid: "8974d16c-0f07-4191-b401-b1eae1561d3e"
  errors: [
    start_at: {"can't be blank", [validation: :required]},
    end_at: {"can't be blank", [validation: :required]},
    cutoff_at: {"can't be blank", [validation: :required]}

I’m wondering how, using Liveview, I can populate the remaining date/time input fields with the calculated DateTime values on the changeset. I assume, that I’ll also need to convert the #DateTime<... values to _at_date and _at_time string values as seen for open_at_date.