Get diffrent 2 times in jqueyr by click

Get diffrent 2 times in jqueyr by click

Hello guys, i'm creating cms which calculate diffrent when the employee come in in the office, but now i'm going to calculate diffrent time by event click when employee loggin and click the button come in but i always get Nan result in jquery, 

You can see this demo

already googling here but there should add date other hand i only have hour:minute:second, thanks for comment and answer