The text does not really specify the time that has elapsed since Mr. Berry was burned, but we can assume it has been a little while because Mrs. Berry states in chapter four that "the fire has burned him too bad. But he understands all right." She also covers him and he cannot stand any clothes touching him (supposedly, since she uses a sheet). It seems like his wounds are healed over, but still sensitive. Further though, a little while later when the children are back on the road, Mama says
'The Wallaces did that, children. They poured kerosene over Mr. Berry and his nephews and lit them afire. One of the nephews died, the other one is just like Mr. Berry.' She allowed all this information to penetrate the silence , then went on. 'Everyone knows they did it, but nothing was ever done.'
From this the reader can conclude that some time has elapsed, or at least some time so that the black community had enough time to figure out who the perpetrator was and to draw some conclusions. Mr. Berry also talks to Mama, which indicates that his pain is present, but bearable. The first mention of the nephew's death is ,of course, made in chapter two during the church service.