Simple.

Outside of Aurora's warp field, time was progressing at the same real time she was experiencing in the alternate universe. Inside the warp bubble, time was slowed. From the outside of the event, Aurora would have been experiencing that 57 seconds over a two day period. The instruments self corrected when things like stellar drift and planetary positioning was measured against recorded time.

 

Which was likely the reason Kara got a laugh out of it. The two day time lapse kind of heavily suggested that her experiences were not the result of hallucinations; but that at least in one universe, her family was alive and well.....and she'd managed to kick herself in the ass for almost screwing up a good thing. Plus the fact that in breaking the link between the two Kara's, the only physical evidence that would -prove- what had really happened was gone.

 

Plus you could add the fact that her baby -survived- going to warp in a nebula, on the leading edge of a proto-matter explosion. Not bad for reconditioned gunship.....

 

And if you didn't watch Aurora, you might want to give it a whirl, Acadia. No MarySue whatsover. Just a story set in the Classic Trek universe, and Starfleet is quite secondary. And you never see the Enterprise, or any of the classic cast.