Hello mr_rob,
Without vCenter, your only feasible options are to use PowerCLI or Crontab - an example of Crontab to set this would call 'vim-cmd vmsvc/power.on <VM-ID>' written to a .sh file at whatever time interval you want, could even do a for loop against 'vim-cmd vmsvc/getallvms' to run this against all registered VMs, of course a second line with power.off will be needed.
Do note that if just doing it for one VM then the VM-ID would have to remain static which means either don't un-register/re-register the VM in inventory (or change the ID in the script if you do).
Bob
