It depends on many factors such as the size of the virtual machine, the available system resources, the I/O depending on where the various virtual machine files and snapshots are stored, etc. However, because this kind of erasure is handled in a live environment with other running virtual machines, a very popular feature of Blancco Virtual Machine Eraser is to set a maximum speed of MB/s so that not too many system resources are dedicated to erasure. This can be configured in the config file which is delivered with every installation package.