About 3-7 days. Different situations need different time. If there is no hole in the inner wall corresponding to the depression, it is necessary to touch and weld some circular gaskets on the surface with a repair machine, then pull them out with a pull rod, then knock off the welded gaskets, grind them down, and fill them in with ash and paint, which is actually very internal injuries. If it's not very depressing, just polish the surface and fill it with ash and paint. But the ash can't be thick. If it is thick for a long time, it will crack.