The distance between them in the Dhuhr prayer is the amount of time it takes to pray four rak'ahs, reading about ten verses in each rak'ah. This is not a strict requirement; rather, one should do what is appropriate for the congregation while considering the preferred time for Dhuhr, which is to delay it in the summer and to hasten it in the winter. See: Fath Bab al-'Inayah 1: 202.