There is no clearcut answer to this one.
Some say the answer is "NO", as in "No I cannot guess the riddle". That is a pretty unsatisfactory answer if you ask me!
Some say the answer is "time".
-when polar bears are born, they are yellow. in time, they turn white
-time and time again, we humans cry
-in time, guys gotta go pee...
-in time, a girls have to comb her hair.....
-in time, celebrities do something stupid.
-in time, a child can grow up handsome (like a celeb)
-in time, on an oven, pancakes turn brown
-in time, champagne bubbles in its process of being made
-if you stare at a clock, it goes so slow, so you will "pop"