Student or Learner
Are both equally correct: These five days passed by/went by in a flash.
Maybe it's better to use "have passed/gone"?
These five days have passed in a flash.
Ofcourse you can say;These five days went by in a flash.
As because "go by" is a phrasal verb meaning: to move past, in space or time(five days): Hardly a day goes by when I don't think about her