What if a candidate notes that web hits can come from all parts of the planet and every timezone and therefore "same day" for a particular end user does NOT overlap with the "same day" of the log files and thus immediately throws into question the meaning of '(a) they came on both days'. Many users could visit the site multiple times in one of their days, but recorded as two separate days in two separate log files. This certainly adds some complexity to the question and might not even be something the interviewer considered in the first place.