Oct 19 (Reuters) - Ladbrokes owner Entain (ENT.L) said on Tuesday rival DraftKings (DKNG.O) has until Nov. 16 to make a formal offer to take over the British sports betting and gambling firm, following a $22.4 billion proposal from the U.S.-based company last month. London-listed Entain said it had sought the extension from Britain"s takeover regulator since the two companies were still in talks over the terms of any possible deal, including plans around its BetMGM joint venture with MGM (MGM.N).