Does Mnemonic Enhancer give you extra spells the next day?

Question

The 4th level spell Mnemonic Enhancer seems a bit weird and a bit useless:

• Burn a forth level spell to get back a third or lower spell you cast the previous round.
• You prepare up to three additional levels of spells (cantrips count as 1/2 level)

However the duration for this:

the spell or spells prepared or retained fade after 24 hours (if not cast)

appears to indicate you could potentially cast this before your nights rest and then, the next day, have those extra spell levels at your disposal, however the clarification line:

You prepare and cast these spells normally.

Possibly counters this. (Although I believe it refers to how you can prepare those spells, ie you still have to sit down and learn them)

So:

Can a Wizard cast Mnemonic Enhancer before resting, prepare those spells and the next day have those three extra levels of spells for all of the next day (minus 8 hours) ?

Or is the only effective way to use this to have it in a scroll or a wand (therefore giving you extra slots without sacrificing the 4th level slots for lower level ones)

Answer 1

Yes, he can.

As per PFSRD,

Until he prepares spells from his spellbook, the only spells a wizard has available to cast are the ones that he already had prepared from the previous day and has not yet used. During the study period, he chooses which spells to prepare. If a wizard already has spells prepared (from the previous day) that he has not cast, she can abandon some or all of them to make room for new spells.

There is no obligation to drop those extra prepared spells; moreover, you could change your selection of additional spells prepared (but not the selection of spell slots they are in).

As a side note, a scroll or wand of Mnemonic Enhancer (or, rather, the retain option of the spell) would not be terribly effective, since you must cast it on the round following the casting of the spell you wish to retain.