Go into manage > posts and find the post. Look at the timestamp in the left of that line under “when”. Is it off on day or time? If so, open the post for edit and then in the lower right under timestamp, adjust the timestamp to when you want the post to appear. Also go into options > general and look at the UTC adjustment and make sure it is correct for you local time (your calculated time is below the field for default time format to the right of “output:”).