Well, as far as i know, if you graduate in MAY ... the maximum u can extend to start ur OPT is JULY. However, you cannot apply for H1 until the next year of April. If your H1 gets approved, the starting day of H1 will be October. So, the situation is - Your OPT expires on JULY but ur H1 will start from October only. There is clearly a GAP of 3 months during which you can't work (i think) and you might have to join college to be in status.... This is just what i have heard from others as well. So, check with experts. Good luck!