look for this file dude "skill_cast_db.text"
you can locate this here: rathena\trunk\db\re\
// Structure of Database: // SkillID,CastingTime,AfterCastActDelay,AfterCastWalkDelay,Duration1,Duration2,Cool Down,Fixed Casting Time
//-- RK_DRAGONBREATH 2008,0:0:0:1000:1000:1000:1500:1500:2000:2000,0,0,10000,0,0,500
so in this case dragon breath's fixed cast time is "500"