Bydd yr ymchwiliad, oedd i barhau am oddeutu pum mis, bellach yn dechrau ar 31 Mawrth 2017.  Bydd yn edrych ar bob agwedd ar Brosiect Coridor yr M4 o amgylch Casnewydd, ac yn ystyried yr wybodaeth ddiweddaraf fwyaf cywir, yn ogystal â phob awgrym arall a ddaw.
The inquiry, which is expected to last around five months, will now start by 31 March 2017. It will examine all aspects of the M4 Corridor around Newport Project and take into consideration the most up-to-date and accurate information, as well as all suggested alternatives.