Hi Edy,
This is actually a Tricky question, Since its an iSCSI Storage it depends on a lot of factors like Network Bandwidth, Load on Storage and your storage processor and storage Model.
In a Nutshell : I have seen 512GB to take around 3- 5 Hrs to complete and If your storage is VAAI Supported and Enabled, It could take a lesser time.
Thanks,
Avinash