I think that the object in question is a small flail with a cylindrical head. If the object is a scroll case, then why is it attached to a rod by a short length of rope or chain? And sure, the official North Star photo of the model shows the object painted silver/steel and gold as one might expect of a fancy scroll case or reliquary, but the painter may have been confused about the identity of the object.
Clues to the object's identity include the flail's origin and the symbolism of the flail in Western history and culture. The flail was derived from a medieval farming tool (used to thresh grain), which like the flail on the Chrono apprentice's belt, had a head that was elongated rather than round. Chronomancers manipulate time. Famers used the flail in their practice of agriculture, which is a human activity that has always been governed by the seasons. And seasons are essentially long periods of time.
In ancient Western mythology there exists a strong symbolic connection between farming tools and time. In Greek mythology the Titan Chronus is the patron of the harvest. As such he is often depicted holding a sickle or scythe (farming implements). The Romans turned Chronus (i.e. Saturn) into the god of the harvest and time. Like his earlier incarnation, Saturn was often depicted holding a scythe, which like the flail is a farming implement.
I would also point out that the Chrono wizard is armed with two weapons, a staff in her hand and a sheathed sword. The Chrono apprentice also has a staff in his hand, and if the object in question is a belt, then like his master, he too is armed with two weapons.