I would agree with what Brent Bean advises....you've got to take apart & shake the bees off the SBB into the hive, otherwise they'll just stay under there for who knows how long because they can communicate through the screen with the bees inside.
I've had this same problem. It's very hard to get bees , which haven't oriented to the entrance, out from under a SBB because they're receiving queen phermone smell from the bees inside ...through the screen. For this reason, when I was making my own SBB, I would make them with two screens.....the top one permanent and the lower one interchangable with a solid mite tray which could slide in & out. When you ran it for ventilation , there would be two screens about 3/4" apart, therefore no bees could communicate or exchange anything through the SBB. Works great!