so instant spells require preparation just like other spells?
class1, class2 and class3 are different?
No, instant spells do not require preparation. But my interpretation was that they still take some time to cast. Casting and preparation are different. Preparation is when you prepare a spell in a round before you can cast it, in a round when the spell will not resolve. Casting it on the other hand occurs in the round when the spell resolves. All spells take time to cast, but not all require preparation. The ones that don't require preparation are called instantaneous.
On a side note, I think part of the confusion here is the use of the word 'instantaneous' itself. I think a better word would be 'Quick'. Instantaneous implies no time at all, but it sure seems like even an 'instantaneous' spell requires
some time to cast. The same applies to actions RMU calls 'instantaneous': they sometimes cost an action point, or about 1.25 seconds. So the confusion here I think would be solved if we renamed 'instantaneous' to 'quick'.
spells like bladeturn must have zero prep to work right? or is there still prep and the spell is 'stored' until its needed?
Yes, Bladeturn is an instantaneous spell: it requires no preparation. Beyond that, things probably get a little fuzzy I think: Bladeturn has been one of those spells people argued about because it could be interpreted to have an infinite duration (i.e. till someone attacks you), since the duration was IIRC never specified in the original Spell Law. Some people argued it should only last for a round, others that it would last longer. I think there was an official ruling about this, but can't remember what exactly it said about the duration. I don't know what RMSS did to handle that, but I think RMU should give a set duration to clear that up.
Here is the description of the Deflections spell (which works in the same way as Bladeturn) in RMU beta:
"Caster can deflect any one missile that the caster can see and which passes within the 100' range of this spell; this causes 100 to be subtracted from the missile’s attack."
Here is how I would word it (additions in italics):
"Caster can deflect any one missile that the caster can see and which passes within the 100' range of this spell
during the round in which the spell was cast;
the spell effect causes 100 to be subtracted from the missile’s attack."