Force oracle to evaluate one of my predicates 1st

INSERT INTO call_analysis
SELECT folder_fk, 
	   decode(to_char(date_call, 'HH24:MI:SS'), '00:00:00', 'Unknown', to_char(date_call, 'HH24')) As Hour,
	   servnum,
	   serv_dialled As Dest_Servnum,
	   cat_desc,
	   sum(pct / 100) AS Qty,
	   sum(charge * pct / 100.0) as cost,
	   avg(decode(duration, '', 0,duration)) AS AVG_Duration,
	   a.customer_fk
FROM (
	 SELECT NVL(serv_split.customer_fk, service.customer_fk) as customer_fk,
	 service.servnum,
	 NVL(pct, 100) AS pct,
	 serv_type_desc,
	 NVL(description, 'Unallocated') AS description
	 FROM service
	 LEFT JOIN serv_split ON service.servnum = serv_split.servnum
	 JOIN serv_type ON serv_type_fk = serv_type_pk
	 LEFT JOIN service_allocations ON service.servnum = service_allocations.servnum
	 LEFT JOIN allocation_categories ON allocation_categories.allocation_category_id = service_allocations.allocation_category_id
	 ) a
JOIN customer ON a.customer_fk = customer.customer_pk
JOIN ui ON a.servnum = ui.servnum AND NOT EXISTS (SELECT 0 FROM analysed_mids WHERE mid = ui.mid)
JOIN dt ON ui.mid = dt.mid
join cat on ui.cat_ref = cat.cat_ref
GROUP BY folder_fk,
	  	 decode(to_char(date_call, 'HH24:MI:SS'), '00:00:00', 'Unknown', to_char(date_call, 'HH24')),
		 servnum,
		 serv_dialled,
		 cat_desc,
		 a.customer_fk

JOIN ui ON a.servnum = ui.servnum AND NOT EXISTS (SELECT 0 FROM analysed_mids WHERE mid = ui.mid)