My wizard has just woken from a long rest and is thinking about what spells to prepare for a new day of adventuring. The PHB says on p.114:
You prepare the list of wizard spells that are available for you to cast. To do so. choose a number of wizard spells from your spellbook equal to your Intelligence modifier + your wizard level (minimum of one spell). The spells must be of a level for which you have spell slots.
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.
As a 1st level wizard with 16 intelligence I have 4 1st level spells I can prepare.
So my question is, can I prepare 3 spells in the morning and then wait until I see a situation that calls for a particular spell and spend 1 minute studying my spellbook to learn that spell, provided that I still have a 1st level spell slot left?