How do prepared casters use metamagic rods?

Question

How do prepared casters like clerics and wizards use the metamagic rods?

• Are they only able to use the rod during the actual act of casting the spell?
• Are they able to use the rod when preparing spells so that their spell is prepared as the metamagic'ed version?
• Both are valid methods?

Answer 1

Only the first option is valid: Having the metamagic rod does nothing while preparing spells. They are only effective if the caster is holding the rod while casting the spell.

From d20pfsrd:

Metamagic rods hold the essence of a metamagic feat, allowing the user to apply metamagic effects to spells (but not spell-like abilities ) as they are cast.

Emphasis mine.