@JeremyECrawford If a spell has a longer casting time, do you have to complete its time requirement in order to successfully cast the spell
— Samual Engler (@BiiigSam) August 28, 2015
See the "Longer Casting Times" section of the Player's Handbook (p. 202) for how such casting times work. https://t.co/3aVpF5oz1c
— Jeremy Crawford (@JeremyECrawford) August 30, 2015