Portent and spell preparation: which comes first?

Question

Both the dice rolls for the 2nd-level School of Divination Wizard class feature Portent and a Wizard's spell preparation occur "when you finish a long rest". Which comes first - or can a Wizard PC choose?

The specific problem here is that if Portent's dice rolls happen before spell choice, the PC might choose different spells. If not, they cannot use that information when they make spell choices.

(PHB, p. 114)

You can change your list of prepared spells when you finish a long rest. Preparing a new list of wizard spells requires time spent studying your spellbook and memorizing the incantations and gestures you must make to cast the spell: at least 1 minute per spell level for each spell on your list.

(PHB, p. 116)

Portent. Starting at 2nd level when you choose this school, glimpses of the future begin to press in on your awareness. When you finish a long rest, roll two d20s and record the numbers rolled.

Answer 1

Portent comes first

Because preparing spells does not happen at the end of a long rest - it happens at the end of time spent preparing (as noted in the question).

You can change your list of prepared spells when you finish a long rest. Preparing a new list of wizard spells requires time spent studying your spellbook and memorizing the incantations and gestures you must make to cast the spell: at least 1 minute per spell level for each spell on your list.

The process looks like this:

1. Thoth Amon finishes a long rest.

2. Lin, Thoth Amon's player, rolls Portent dice.

3. Lin decides to prepare different spells - four first level, one third level and one fifth level.

4. Thoth Amon spends 12 minutes preparing those spells.

Most tables include the spell preparation time in the 8 hours of rest, for simplicity of time tracking.