don't use the date class, use the timer class.
var feedTimer:Timer=new Timer(5*60*1000,0);
feedTimer.addEventListener(TimerEvent.TIMER,feedF);
feedTimer.start();
// whenever vpet is fed, apply a reset() and start() to feedTimer:
function beenfedF():void{
feedTimer.reset();
feedTimer.start();
}
function feedF(e:TimerEvent):void{
// a feeding was missed
}