Among all the residential areas in Delaware, how many of them implement daylight saving?
"Delaware" is a county; implement daylight savings refers to daylight_saving = 'Yes'
SELECT COUNT(T1.zip_code) FROM zip_data AS T1 INNER JOIN country AS T2 ON T1.zip_code = T2.zip_code WHERE T2.county = 'DELAWARE' AND T1.daylight_savings = 'Yes'