If someone is given a federal charge while already being an inmate, how long until the inmate is moved to another facility?

The federal charge would have to be adjudicated in District Court to know the outcome. The inmate will be held in their current location to serve out the remainder of their sentence. During the court proceedings, the inmate will be transferred to a county jail in the jurisdiction where the indictment was handed down to face the federal charges. The time they do counts toward their accrued time.