my uncle (British passport holder)wants to visit china.how many days will the process take

Processing time is around four working days if your uncle have all the right documents.

thanks for your reply.
we completed the process online with all required documents.
i hope this also takes less time

he applied for ivisa.
i read from a website that the family member must be parent,son,daughter,grandparent,grand son,spouse,son's spouse,parents-in-law for S2,but is my mother's brother who wants to attend my graduation ceremony.does this make any effect on visa approval?

Your mother's brother cannot apply for an S2 type to visit you in mainland China. Try to apply for a tourist L type for that.