Probably close to the same amount of time it took to do the backup, unless the read/write speed of the two devices is vastly different. This is assuming the backup was done on a drive other than the one 3CX is operating on.
I did perform the backup a couple of days ago, it only took 20 seconds at the most. We are running on a v18 system. It was a restore on an active system hosted by 3CX. Thanks all for the input.