I need to write python scripts to automate time configuration of Virtual Machines running on a ESX/ESXi host. 
I don't know which api to use...
I am able to find to python bindings for VMWare apis viz. PySphere and PyVmomi.
Could anyone please explain what is the difference between them, which one should be used?
Thanks!
Also pyVmomi directly corresponds to the vsphere Managed Object browser.
So get to the MOB on the vcenter, figure out what properties you need, the methods as well and the 1 to 1 name convention from pyvmomi helps you achieve what you want.
(in short, you learn about vsphere api and are good to go with pyvmomi, no mapping in the head needed)
What is the Difference between PySphere and PyVmomi?