I personally think it's worth it, it gives backstory to what happened when Zu was seperated from her friends after they left east river and also gives some extra information about the state of america after IAAN.
It doesn't really matter when you read it. It doesnt give any vital information needed to understand Never Fade. Its mainly just background info thats very briefly brushed upon in ITA
I would say it's worth reading, but it isn't really important for the main plotline, so you can read the main series first, and the novellas after that.