How to update data in ASP application after some time period

Question

My application have to maintain employee attendance details daily.

In the Application, i am getting employee IN Time and OUT Time by using IN & OUT Buttons.

The employee has to Click IN button when he enter in to office and similarly he Click on OUT button when he leaving from office in application.
By using OUT Time button click, i maintain the attendance details on that day.
My requirement:
Suppose the employee is not came to office(absent), i will not get IN&OUT details for that employee on that day.
so after some time suppose After 6 PM office closing time,the application will have search all employee IN and OUT times, then and it will automatically store(send data as Absent to database) for those employee who are absent.
How can i achieve it