From Longman Dictionary of Contemporary Englishtime fliestime flies (also the hours/the days etc fly)PASS/TIME PASSING used to say that a period of time seems to pass very quickly ‘Is it midnight already?’ ‘Well, you know what they say – time flies when you’re having fun!’time flies by The following weeks flew by, and soon it was time to leave. → fly
Examples from the Corpus
time flies• Is it 5:30 already? Boy, time sure flies!• Is Richard eight already? Doesn't time fly?• There are so many diversions here that the time flies by on wings.• Dearest Jeanette How time flies especially when one is meant to be writing lots of letters.• Think how time flies in periods of intense, purposeful activity.• "Hasn't the afternoon passed quickly?" said Carol. "Time flies when you're having fun."time fliestime fliesused to say that time seems to pass very quickly Time flies when you’re having fun. → timeExamples from the Corpus
time flies• Dearest Jeanette How time flies especially when one is meant to be writing lots of letters.• Think how time flies in periods of intense, purposeful activity.• There are so many diversions here that the time flies by on wings. 