Is there any rule regards how many day to enter china before the end of residence permit?

As a foreign student in Beijing, I am currently holding a 1-year residence permit which ends on 31 AUG 2014. However, I might have to leave China for few weeks then would go back to by mid of July'14. Will this viloate anything regards my residence permit above? For example, is there any regulation i.e. how many days I must enter China before the residence permit ends? Just would like to cross check, thank you very much.