Casting times for priests and wizards are exactly analogous to Speed Factors for weapons; the casting times are between 1 and 9, representing how quickly a wizard or priest can release a spell. The lower the number, the faster the casting.
This represents the fraction of the spellcaster’s six-second personal initiative round that is used to perform the chants and motions necessary to cast the spell. This time is exactly equivalent to the Speed Factor of a weapon. The spellcasting time is varied by an initiative roll that is performed each time a spell is cast.