You could of course use sessions to maintain a users logged in period, but the deleting will need to be handled by a cron executed periodic script.
To do this you would simply need to add a tmie...

in short...
1) not really
2) incase u fry one trying to overclock the chip or just break it
3) thats a major problem and negates any future-proofing plans you may have

I would go for a better...