Given the task definition and input, reply with output. In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What causes changes when they do not line up accurately?, Context: Beginning and ending dates are roughly the reverse in the southern hemisphere. For example, mainland Chile observed DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time. The time difference between the United Kingdom and mainland Chile could therefore be five hours during the Northern summer, three hours during the Southern summer and four hours a few weeks per year because of mismatch of changing dates.

mismatch of changing dates