Factor: my use of the dates in my example were hypothetical to demonstrate what 2 months means; the author didn't actually say on what date his friend resigned. To leave the existing post on Friday 15th August, the friend must submit his resignation letter on or before 15th June. This date was a Sunday, so unless he could do this because his company works that day, the latest effective date was Friday 13th. Now there's an omen.
Julian, legally the 2 companies are separate entities so the requirement to give notice IS valid.