There is no statute that dictates how quickly another county must pick up an inmate being held in another county. You should hire a Polk County attorney and have him try to expedite the situation; or work out the situation.
Richard is correct about a statute, but some counties have policies that will only keep a defendant so long, such as 10 days. Check with the Hillsborough jail what that policy is. Still, it doesn't mean they will let him out just because so much time has passed. There may be other issues as well. Also, you should hire an attorney in Polk County to help you remedy the situation.