Two weeks of waiting is not unusual, and unfortunately there is no guaranteed timeline that either county is legally obligated to meet outside of one specific circumstance.
Inter-county transfers in Pennsylvania happen when the receiving county, in this case Allegheny, can spare two deputies to make the trip to Butler and bring him back. That sounds simple but it depends entirely on staffing availability, scheduling, and how many other transports Allegheny County has in the queue at the same time. Large county jails like Allegheny run transport operations constantly, and a single transfer from Butler is one item on a long list. It moves when resources allow.
The one deadline that forces the timeline is a court date. If your husband has a scheduled appearance in Allegheny County, the receiving county is obligated to have him there for that date. That court date becomes the hard deadline that everything else gets scheduled around. If no court date has been set yet, the transfer will happen on the county's schedule rather than yours.
The practical advice is to find out whether a court date has been scheduled in Allegheny County. His attorney or the Allegheny County court clerk can confirm that. If a date exists, you have a clearer picture of when the transfer will happen. If no date has been set, the timeline remains open ended and two weeks can stretch to four or six without any rule being broken.
Staying in contact through letters is the most reliable way to keep communication going during the transfer window since his phone access and account information may not carry over seamlessly between facilities.