I don't think that you have to wait. You can specify the new name using the Set-VM -Name parameter: The following works for me:
PowerCLI C:\Users\Robert> $VM = Get-VM -Name test1
PowerCLI C:\Users\Robert> $VM
Name PowerState Num CPUs MemoryGB
---- ---------- -------- --------
test1 PoweredOff 1 0,250
PowerCLI C:\Users\Robert> Set-VM -VM $VM -Name test2 -Confirm:$false
Name PowerState Num CPUs MemoryGB
---- ---------- -------- --------
test2 PoweredOff 1 0,250