Boyfriend has a detainer in montgomery county and a warrant for a FTA in bucks co. After his detainer is either certified orhe finishes out his back time in philly, how long can they hold him in philly before he has to be released if neither county picks him up? Or how soon can we expect to wait before being transferred to these counties?

A few weeks is not uncommon. He does not "have to be released" if he is keep to long, he can file in court asking to be released.