Translation:It takes two days.
Apparently, 間 is optional for duration of days, except for the duration of 1 day, which is required to drop the 間.
Nevermind, it just hit me that かかります is just one word. か is not a particle.
why it can not translated as "it will need two days"? what is the different? it still the same, right?
You could write "It will take two days". There's no word meaning "need" in this sentence.