I am sorry to hear you are having problems with setting the timezone for your virtual machine.
This should be a very simple process since it is pretty much a copy of VMware Studio's vApp build process.
However, please be careful in the spelling and syntax of the XML - the code snippet is a direct copy from my virtual machine so should be fine. For some bizarre reason, this parameter does NOT need a period between vami and timezone. In fact, the current VAMI code will ignore your parameter if it finds a period between the two. Unusual behaviour, but the VAMI code is pretty easy to understand and this is how it is written.
It is easy to verify the process has worked at deployment time by interrogating the environment file for your VM.
From a shell prompt - /opt/avaya/bin/ovfenv - should display all of the key/value pairs that are presented to your VM by vCenter at boot time.
You should see - [vamitimezone]= - with a suitable value ( other than UTC ).
There is no need to write any code to process this value, since the existing vaos daemon will extract and apply this value using VAMI.
Hope this helps,
Robin.