I'm guessing that this is either (1) an internet cafe scenario, (2) a corporate network scenario, or (3) a prank that you wish to play on people.
If (1) get hold of some proper interenet cafe software. As you metion "customer" this seems to be the most likely option.
If (2) use the facilities built into Windows Server to manage logon times.
If (3) - and the request for a solution using a specific language makes me think this is most a possibility - forget it.