Practicing your scales in sixes and thirds is essential to playing the accordion.  An even better idea is to practice in time with a metronome.  There are various metronome programs available for free on line.
For someone who wants a super-metronome that can be programmed to do anything you want, I suggest the VKO Mundobeat. 
Whatever program you use, playing in time with a metronome will show you if you really know the scale or not. 
To increase your speed, try increasing the speed of the metronome a little each day. 
Other metronome programs.
Metronome on line

Metronome for PC