Задачку решил, если кому то будет полезно оставлю решение здесь.
SELECT
IF(p.price_noch > 0,
IF(TIME(NOW()) > TIME('13:00:00'),
IF(p.price_uah > 0, IF((p.price_noch/k.kurs) < p.price_in, (p.price_in+(p.price_in*0.1))*k.kurs, p.price_noch), p.price_noch*k.kurs),
IF(TIME(NOW()) > TIME('08:00:00'), IF(p.price_uah > 0, IF((p.price_noch/k.kurs) < p.price_in, (p.price_in+(p.price_in*0.1))*k.kurs, p.price_noch) ,p.price_noch*k.kurs),'NULL')
)
, 'NULL') AS price, TIME(NOW()) AS date
FROM `product` p, (SELECT value AS kurs FROM kurs ORDER BY kurs_id DESC LIMIT 1) AS k WHERE 1