Does an apple cultivar ripen at the same time every year?

Not necessarily. Time of apple ripening is affected most by bloom date and growing season weather. For example, McIntosh typically ripens 125 Days After Full Bloom (DAFB), but can range from 115 to 135 DAFB. There are formula(s) for determining harvest timing, for example, this one for McIntosh from Cornell University. In any year the best indicator of maturity and harvest timing is a combination of flavor and fruit background and over-color, but the starch-iodine index test is also very useful in determining readiness for harvest.