It means that as you are having fun, you're also basically "wasting" your time. Without even realizing, it can be past a few hours and you're at your home having a party and then you realize that you've wasted so much time having fun that you didn't even notice that time was ticking by. This is just an example.
He sought to emphasize the historic nature of the events at Pearl Harbor, implicitly urging the American people never to forget the attack and memorialize its date.
