I've noticed that Wizards, Clerics, Druids, and most other spell-casting classes (With the exception of Sorcerers) spend at least 1 hour Studying or Meditating to regain their spells.

What I want to know is that if I (As the GM) used an encounter to interrupt the preparation time of the party halfway through, will the party have any spells available to utilise? IF they do, is there any RAW method to restrict which spells they will have? (Such as no spells requiring an attack roll, or spells that deal damage.)

Is there anything I can do to force a Sorcerer or other spontaneous caster to contend with the same issue?

Backstory:

I want to introduce a recurring villain, who will be involved as a plot device for quite a while before eventually transforming into a BBEG. Said villain will have quite high DR-which will prevent melee characters from being able to kill him, but looking for a method to surprise the casters, forcing them to look for alternate methods to escape. (Particular villain has yet to be decided, but I don't think it would help the answer at all.)

I'm not looking to kill the PCs, at all. Just want a way to scare them a bit, making them think about what they are actually doing.

I have considered an anti-magic field already, but I think this would lead the party to kiting, rather then looking outside the box.

I've noticed that Wizards, Clerics, Druids, and most other spell-casting classes (With the exception of Sorcerers) spend at least 1 hour Studying or Meditating to regain their spells.

What I want to know is that if I (As the GM) used an encounter to interrupt the preparation time of the party halfway through, will the party have any spells available to utilise? If they do, is there any RAW method to restrict which spells they will have? (Such as no spells requiring an attack roll, or spells that deal damage.)

Is there anything I can do to force a Sorcerer or other spontaneous caster to contend with the same issue?

Backstory:

I want to introduce a recurring villain, who will be involved as a plot device for quite a while before eventually transforming into a BBEG. Said villain will have quite high DR-which will prevent melee characters from being able to kill him, but looking for a method to surprise the casters, forcing them to look for alternate methods to escape. (Particular villain has yet to be decided, but I don't think it would help the answer at all.)

I'm not looking to kill the PCs, at all. Just want a way to scare them a bit, making them think about what they are actually doing.

I have considered an anti-magic field already, but I think this would lead the party to kiting, rather then looking outside the box.