You can modify the VISA timeout value to anything you want. If you're still experimenting in MAX, select the Property Node (Write) and select the attribute Timeout Value. In LabVIEW, the VISA property node can be found on the Instrument I/O>VISA>VISA Advanced palette. This should enable the VISA Read to return much quicker. I'm not sure about stopping the measurement of the instrument. You could try sending the ABORT command.