Right time to apply resident permit for z visa holder

Hi I’m Sanjay from india
I got work permit from my employer and it is issued on 22nd December 2017, and written that it is valid for 3months from issuing date but I want to apply for z type on first week of feb 2018 and I want to enter China in first or second week of March 2018 but my employer said that I should enter China in at least last week of feb because my work permit is vaild until 21 March 2017 and I should get resident permit and medical examination before the expairy of work permit.
So please give me the suggestion and whole process to handle my problem