It's a subtle difference. 'We will go in five days' is 'हम पांच दिन में जायेंगे' and means that we will be going five days from now. 'हम पाँच दिन बाद जायेंगे' means that we will go five days from the time dictated by the context. Eg. 'वे कल जाएंगे। हम पांच दिनों बाद जाएंगे।' means that they will go tomorrow and we will go five days after that.
Hair-splitting aside, I do think 'We will go in five days' should probably be an accepted translation here.