Hi, need to understand whether we need to hire any Guide to visit China Wall or not?

Of course it is possible to go there without a guide and many overseas tourists have done that. But prepare well beforehand.
About the time required, it varies based on the section of wall you are going to visit. If it is Badaling or Mutianyu, you need more than half a day. If it's Jinshanling, Simatai or even further sections, you may need one or more days.