You want to find the number of visits IN BETWEEN 12:30 PM and 6:45 PM
there some visits already recorded before 12:30. These visits are visits that you want to exclude but are included in the TOTAL visits
Before 12:30 the website has 1200 visits and at 6:45 the website has 14000.
You can do 14000-1200 to find the number of visits in the time frame between 12:30 and 6:45
ANSWER 12800 visits