From how I understand the rules, once you enter a division 1 school, your eligibility clock starts, and you have 5 years to use your 4 years of eligibility.
Sometimes with football players, for example Robert Griffin III, they enroll a semester early, so the spring of what is normally their senior year. This is not that uncommon, and seeing a few at a big time university every year is not uncommon. Unlike Robert Griffin III, not all of these players will leave school early.
What happens if a player enrolls in a university a semester early, and then somewhere along the line redshirts and needs to stay for a 5th year. Would he be eligible to play in a bowl game after first semester ends, or would his eligibility expire first semester of his 5th year?