It means that the time is going faster then you thought, and that it can have consequences.
You better get the butter, time is a thief.
Noun.) a killer that stabs his victims ( mostly women) 37 times in the genitalia, then steals their ovaries.
"The pocket thief stole that dead woman's ovaries!"
Someone who steals your lighter.
"Check out my cool new lighter!"
"Don't leave it laying around. Craig's a pocket thief, man."
The person up train of you on the sushi train that steals your chosen plate or plates.
Differs from a sushi hog and sushi ninja by quantity and selectivity.
-- Tina Yothers just sat down and she has already robbed me twice. What a Sushi Thief!
A stupid person who tries to steal your best friend by hanging out with you and your best friend.
For example they are the only person who can sit next to your best friend.
Rulie aka friend thief always has to sit next to my best friend Gilia.
Someone who steals something visually by looking at it
That eye thief over there is looking a lot.