Spell Casting

Players Handbook (page 100)

Most spells can be cast during the course of a single melee round, although some - particularly high level ones - require more time. Casting a spell requires certain actions, and if these are interrupted, the spell cannot be cast and it is lost from memory. A good example of this is a magic-user about to cost a fireball spell being struck by on arrow when in the midst of the spell. Magical silence or physical gagging will prevent verbal (V) spell completion. Magical immobility prevents any spell casting. Physical restraint, including grappling, grasping, binding, etc. prevents proper somatic (S) spell completion, for gestures must be exact and movements free and as prescribed. Despite these restrictions, there is no doubt that spells in general are potent offensive and defensive weapons, providing the caster does not hesitate, i.e. he or she must know which spell is being cast when the melee round begins.

House Rule

Memorising a known spell (ie loading into memory) takes at least 30 minutes (for the most basic spells) of pure concentration (study or praying) if not already loaded. Assume 30 mins per level for each spell. e.g. So 2 second levels spells and 1 first level spell, will take at least 2 and a half hours concentration, sleep, etc. Therefore no walking, talking, dungeoneering, drinking, etc.
Casting spells takes the defined segment, round or turn length.
Casting any spell requires the caster to be in the prescence of their Aetherium Focus