It depends on the company, how you are leaving and if they already have someone lined up to handle your duties. From my experience from departing an employer, one gave me 90 days (reduction of working force), another one wanted me to leave immediately (gave them my two weeks notice/mutually agreed to part that day) while my last job let me do my last two weeks before I join my current company. Some companies want people who are leaving to be gone ASAP regardless of the circumstances while some will work with them until the last day. Since Shannon has a major impact on the show, they probably wanted him to stay until the finals because that the last main sporting events for the next few months.