MySQL - case when

SELECT
    count(*) AS Count
    , CASE 
        WHEN MAX(ad.updated_at) > MAX(ad.deleted_at) 
            THEN ( 
            UNIX_TIMESTAMP(now()) - UNIX_TIMESTAMP(MAX(ad.updated_at))
        ) / 60 
        ELSE ( 
            UNIX_TIMESTAMP(now()) - UNIX_TIMESTAMP(MAX(ad.updated_at))
        ) / 60 
        END AS DiffTime 
FROM
    tb_m_advertiser ad 
    left join tb_t_application ap 
        on ap.creater_id = ad.id