How Long does it take to copy VMs with VMWare vCenter Converter Standalone?

Still considering whether it will be worth purchasing vCenter software, for now I am getting by with the free tools supplied by VMWare. To clone a new VM from one ESXi host to another, I powered it down and used vCenter Converter to do a VM to VM copy.
The VM I’m copying was about 350GB. When I launched the Task, the Estimated time was 1 hour. After the progress achieved 1%, the estimated time jumped up to 1 day, 18 hours. It remained there as progress reached 2% about an hour later. I came back the next morning about 15 hours later, and the conversion was completed successfully. Very glad it didn’t take more than 1 day or I would’ve had to stop the process and find another way.