I think it depends on the grid points of the calculation. Thus depends on the size of the systems and of-course on the docking area. For instance, if you are performing blind docking for whole protein, it will take some extra time because of extra grid volume. Hope it helps.
Depending upon CPUs, if you use normally 4 cpu it may takes less than 1 min. Also, if size of grid is big, for e.g. 100 x 100 x 100, then it may take 2-5 mins. You need to inspect is the all parameters and protein where you are generating grid is appropriate. I suggest to make one more time preparation of protein and ligand and try for autogrid generation