The translation "free" is only "空", not "有空". Please fix the translation as soon as possible!
有空 means 'have free time'. This sentence is :‘Do you have free time on Saturday?' if you translate from Chinese.
Is 你周六方便吗 okay?
Surely it is.
Why are 你星期六有没有空， 你星期六有时间吗 and 你星期六有没有时间 not accepted?