Hi Mahyar,
If you're using the Lee valves we carry, the time to full-open should be 3ms, as per manufacturer specs (and 2ms if gating air).
Solenoid pinch valves like this one take ~30-40ms to fully open, so the calibration curve can be non-linear.
As a sanity check, I'd print out the valve times that are being generated by the GetValveTimes() function. If your script is requesting liquid amounts beyond the limits of the calibration curve, it can result in unexpectedly long valve-open times.
Generally, I'd try using a 12V DC wall adapter (1.5A, positive-center), especially if you have other power-hungry devices on the USB hub.
I don't have experience running Bpod in Octave - do you see the same issue with our MATLAB software + the latest firmware?
-Josh