Is it permissible for the Imam to delay the prayer in order to complete a lesson?

It is preferable for the congregation to delay the prayer slightly to allow worshippers to gather, as long as the prayer's time does not expire. This is an emulation of the Prophet, peace and blessings be upon him, who used to delay the prayer if the Companions were slow [in gathering] and hasten it if they had gathered, and he would delay Dhuhr due to intense heat. Based on this, there is no impediment to the Imam delaying the prayer to complete a lesson, provided that the optional time does not expire and that the worshippers are not harmed by this delay, due to the Prophet's saying, peace and blessings be upon him: "There should be no harm nor reciprocating harm."