Just give him the entire year.
It's not just physically he has to heal, but he has to heal mentally too. That kind of injuries could affect someone's mindset, and he needs all the time in the world to get back to the mentality that he had before the injury. Otherwise, we will have a 100% physically ready Gordon Hayward, but yet so mentally checked out won't do things because of it.
Let this be the year we develop Jaylen and Jayson. Heal up Gordon, go for it again next year.