Why not "Time has passed so quickly!" ?
I think it should be "the time". The sentence talks about a certain stretch of time.
why not "the time is gone so fast"
Because that's not proper English, and Duolingo is very strict about your English skills even when you're learning a different language.
Nothing wrong saying time has gone so fast
men hvorfor er det ikke "tiden har gået så hurtigt"?
Verbs of movement or change (gå, flyve, løbe, blive, you name it) use a form of være as their auxiliary.
To my knowledge, Swedish and Norwegian do not share this rule. I wonder whether this is an archaicism or example of convergence due to the influence of German, which does share a similar rule.
"Time is on my side ".