Hi @jsardonicus, and welcome to the forum!
Data bindings are part of the form, not of the components themselves, so what you want to do is call self.refresh_data_bindings(). (In fact, that data-binding refresh is triggered implicitly by setting self.item, so you could also just set the 'createdAt' and 'updatedAt' keys of that dictionary before setting self.item.)
Here’s a forum post where I walk through the mechanics of data bindings, which should hopefully help you understand why this is happening (read from the heading “how data bindings work”):
(@david.wylie, I’m afraid you’re off base here. The only thing that isn’t valid until the show event is custom Javascript. Everything else can and should be handled in __init__.)