If you have noticed a discrepancy with the time zone of your visitor log export, check your profile settings. Your visitor log will display the time zone of your (or whomever set up the automated export) profile.
In the top right corner of your account screen, select your profile and ensure that your time zone is correct.
The time zone setting under 'Company' determines the default time zone for all newly added users.
The time zone setting under your own profile determines the display of and exported reports of your visitor log.