By setting the timeout to a negative value, you will effectively disable the timeout.
Perhaps that will avoid the problem you are seeing.
Are you checking if the VM is ready after the deployment ?
In which way ?
There are many ways to deploy VMs, perhaps it would be clearer if you include the code you are using.
When the new VM needs to run through sysprep it might take some time before it is actually ready for use.
I don't see why a Disconnect-VIServer, followed by a sleep before you Connect-VIServer might make a difference.
Just stay with the open session, do the sleep (if needed) and then continue.
But the sleep is not the best way to wait till the VM deployment is ready.
Again, the best method depends on a number of factors.
Is the VM reachable over the network, do you place an eyecatcher somewhere at the end of the sysprep,...