"She's leaving in twenty minutes, but she has not yet packed her bags."
Translation:Elle part dans vingt minutes mais elle n'a pas encore fait ses bagages.
because your knowledge is so limited everything you encounter may seem like an exception, it's likely not an exception. that's true here.
'dans' has 3 major functions.
first, to indicate place. 'dans la chambre'
second, to introduce a time as is done here. 'dans vingt minutes'
third, to give approximate numbers. 'dans les quarante euros
dozens of uses of dans can be found here.