Time flies
Definition 1 of 1
Pro Tip 1/3Positive Vibes
Often used to express a good time speeding by, implying positivity. 
We were chatting and laughing for hours - time flies when you're having fun!
Pro Tip 2/3Emotional States
Used to show how emotions like enjoyment or busyness alter perception of time. 
Once I started playing the video game, I didn't notice how time flies.
Pro Tip 3/3No Negativity
Rarely used in negative situations; mainly for activities enjoyed or engrossed in. 
Even though it was a tough project, time flies when you're completely focused.