Response: It is before they pray the Zhuhr prayer. (Then), after the (mid-day) heat has lessened, they can pray (the Zhuhr prayer). And the meaning of his (sal-Allaahu `alayhe wa sallam) saying:
«Perform the Zhuhr (prayer) when it is cool», [Saheeh al-Bukhaaree, No.538] is that you should do the qayloolah before (the Zhuhr prayer).
And if he were to sleep after the Zhuhr prayer, then it is not considered as the qayloolah.