Time flies when you're having fun.

当你开心的时候，时光飞逝。

《柯林斯英汉双解大词典》

How time flies! I've got to go now.

时间过得真快！现在我得走了。

《牛津词典》

Time is fleeting.; Time flies.

时光飞逝。

《新英汉大辞典》

Smiley got him so the frog was catching flies, and he would catch one of those insects every time.

VOA: special.2009.08.29

The only thing that came to my mind was the old joke that time flies like an arrow and fruit flies like a banana.

NEWYORKER: The Region of Unlikeness

It is amazing how time flies as here we are almost half way through April and it seems as though the dust ha barely settled on our review of Q1 2011.

FORBES: Raising Rates Will Be A Mistake, Stick With Equities

Patrick is worried that the importance of Langham Dome may be lost as time flies by and he feels the creation of a museum is the best way to preserve its heritage.

BBC: Museum proposed at World War II site of RAF Langham