Please make sure that the main account that purchased "A Rift in Time" is set as the owner of the Xbox console or have that account signed in at the same time as the account that wants to access the expansion (secondary one).
I played DDV on Xbox, but for some reason after the release of the last update (Update 15), the DLC "A Rift in Time" became unavailable on my secondary accounts.
Last Updated: 17d