Here is the deal. If this is an ESX Classic - you can set a time zone, If this is any version of ESXi, then the timezone is always set to UTC
1. Check if the timezone on your host (ESX) is set correctly
2. In the guests, open a console or take an RDP session and check the timezone. If the same is set to IST, you will need to manually change the same to CST!
3. In VMware tools, you have an option to synchonise time with the local (ESX). Ensure that is Unset and you use an external (inhouse or public) NTP server to sync time
4. The time you see on the ESX host if you open a vSphere Client to the host is the host time translated to your system time. So if you want host time to show up in CST, change your local desktop (from where you have opened the vSphere Client Session) to CST!
Regards
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