1 hour off = on time
Taking a birth control
pill on time, or one hour early, or one hour late, are all the same time.
In real life, there is no difference among the 3 times, because they are so close together. That means, if one wouldn't take Plan B for taking pills on time, then one wouldn't take Plan B for taking pills an hour late nor for an hour early. (However, other reasons might lead one to take Plan B.)