Did the Cezchoslovakian army have any motorized infantry/artillery units outside the armored divisions? If not the AD would have been operating on their own after advancing more than ten or fifteen kilometers.
According to information I have one additional infantry division, 14th was fully motorize. Corps artillery was more or less fully motorized, additional 6 infantry battalions were fully motorized, AAA was fully motorized and according to data I found units of AT artillery were mostly motorized.
According to data 20% of Czechoslovak army was during mobilization motorized.
However if Czechoslovakia was able to support their own fast division in case of attack? Probably not. After all I believe even military plans called fast divisions mostly to counter attack enemy formations. I don't think big offensive operations were planned. Your guess 15 km would be probably about right and in plans of Czechoslovak army probably sufficient. After all they didn't plan to capture Berlin or Munich. However I have seen some plans for limited offensive against forces of Austria from Slovakia. (Used by one Czech author in his AH novel as game changer

)
Edit: BTW Czechoslovak generality itself accepted motorization of Czechoslovak army was not sufficient!