Query not recognize alias
That's because the WHERE executes before the SELECT. You could try calculating  DELAY inside the WHERE 

WHERE ITK_AR_SBP_ID = 'PEAJU_PP' -- P_WGR_ID 
AND TO_NUMBER(ROUND(ROUND(GET_HS(ITK_OPENED_DATE, 
             SYSDATE, 
             ITK_NORMAL_BEGIN, 
             ITK_NORMAL_END, 
             ITK_WEEKEND_BEGIN, 
             ITK_WEEKEND_END, 
             ITK_FREEDAY_BEGIN, 
             ITK_FREEDAY_END), 
        GET_HS(ITK_OPENED_DATE, 
             SYSDATE, 
             ITK_NORMAL_BEGIN, 
             ITK_NORMAL_END, 
             ITK_WEEKEND_BEGIN, 
             ITK_WEEKEND_END, 
             ITK_FREEDAY_BEGIN, 
             ITK_FREEDAY_END)) - 
        ITK_EXPIRATION_TIME, 
      2) &lt; 0