Time taken to move datastore between luns

Hello there

I need to move a  466Gb VM between datastores using vCenter.

I don't have vStorage Motion, so will need to power off the VM first and then Migrate | Change Datastore.

However, so that I can schedule a time to do this, I need an idea of how long this is likely to take.

The VM is located on a SAN and I will move out of office hours, so the amount of I/O on other LUNS should be fairly minimal.

Can anyone give me a guesstimate on this?

Thanks