Dwell is the number of milliseconds the program tolerates zero decoding before trying the next control channel. I think this only works for Lock Mode = "Dedicated".
You have to acquire the active control channel first, then flip the lock mode over to Dedicated. From that point forward, the program should chase the control channels for that site - even after an exit and restart.
If you want to monitor a different site, take the receiver out of dedicated lock mode.