You can set it in db/pre-re/skill_cast_db.txt for Pre-Renewal:
// Skill Times Database
//
// Structure of Database:
// SkillID,CastingTime,AfterCastActDelay,AfterCastWalkDelay,Duration1,Duration2,Cool Down
//
// CastingTime: time to cast this skill, in milliseconds
// AfterCastActDelay: "normal" delay, character cannot use skills, in milliseconds
// AfterCastWalkDelay: amount of time before character can move again, in milliseconds
// Duration1/Duration2: usually the durations used by the skill, at special cases it is used to hold special data
// Cool Down: amount of time until character can re-use this skill, in milliseconds
Where AfterCastActDelay is the delay (in milliseconds) between skill uses.
