Yes. You can terminate the employee on the day he/she has given resignation, but with his/her last day updated as the date to auto terminate an employee from the system. Until then the employee will have access to the system. 

Please find the article and the video on how to terminate an employee.

Article - https://help.orangehrm.com/hc/en-us/articles/360006315954-Terminate-Employee

Video - https://help.orangehrm.com/hc/en-us/articles/360006532133-Terminate-Employee-with-a-Future-Date-Video-