I make a time in and time out system using php and mysqli, when I click time in, the form submitted a current date and time to the database and that was working properly, so I want to add 8 hours on that to know what time exactly I’m going to time out and I add a diff() function to count how many hours is my overtime if I time out late, but the problem is I when I time out early or when i time out under 8 hours, the result of the diff() function is exactly 8hours

This is my code