According to rules, any spontaneous casting which is affected by a Metamagic Feat has its casting time increased. A standard action increases to a full-round action; a spell that takes longer than that will need one additional full round action.
Hmm... let's assume Daisy Druid spontaneously casts an Extended Summon Nature's Ally. Normal casting time is 1 round, which increases to 1 round + 1 full-round action. Which means... what exactly?
A full-round action consumes both your standard action and your move action, but still happens on your initiative, as far as I know.
An action with the duration '1 round' keeps you busy until your initiatitive in the next round.
So, the result would be that the critter appears on the druid's initiative in the round after the summoning... with the druid having spent her non-swift actions for said round. Correct?
As another question... what 'extra time' do I have to apply when meta'ing a spontaneous spell of shorter duration than 'one standard action'? Can I meta Swift or immediate spells without any increase in casting time?
Daisy Druid starts to cast a 1 round cast spell on her turn. She can take a 5 ft. step or a swift action before that.
At the beginning of her next turn, she takes a full-round action. After that, the spell goes off and the summon acts immediately. She can still take a 5 ft. step or a swift action afterwards.
So, the result would be that the critter appears on the druid's initiative in the round after the summoning... with the druid having spent her non-swift actions for said round. Correct?
Yeah.
As another question... what 'extra time' do I have to apply when meta'ing a spontaneous spell of shorter duration than 'one standard action'? Can I meta Swift or immediate spells without any increase in casting time?
Unfortunately, the rules don't cover this at all. The only cast time mentioned is a standard action and "spells with a longer casting time". When the original metamagic rules were written in 3.0, the concept of swift/immediate actions wasn't implemented yet.
If its normal casting time is 1 action, casting a metamagic spell is a full-round action for a spellcaster that chooses spells as they cast them. For spells with a longer casting time, it takes an extra full-round action to cast the spell.
So while 3.5 added "standard action" instead of simply "action", we still don't fully know what to do with swift action spells and metamagic. The simplest option is to cast a swift action spell as a full-round action, but that's a bit extreme. A balanced option might be to let it work as a standard action. Either way, it should be slower than a swift action to use metamagic on a spontaneously cast spell.