Just deployed a domain controller and wanting to disable timesync at the VM hardware settings on a ESXi 6.5 host.

I noticed that there is no ability to “add row.”

Turns out you have to power down the VM first before you can add row(s).   My memory may be failing me, but I recall being able to do this hot with the thick client.

 

Long story short, power down your VM before making parameter changes with Web Client.