virt-builder can usually build out a disk image in 15-60 seconds if the template has already been downloaded and you're running on baremetal. Might be 120 seconds if you have to use nested KVM or TCG.

  $ virt-builder fedora-33
  [   1.5] Downloading: http://builder.libguestfs.org/fedora-33.xz
  [   2.3] Planning how to build this image
  [   2.3] Uncompressing
  [   8.6] Opening the new disk
  [  13.8] Setting a random seed
  [  13.8] Setting passwords
  virt-builder: Setting random password of root to mZbPJw9d1ZHgowBk
  [  14.8] Finishing off
                   Output file: fedora-33.img
                   Output size: 6.0G
                 Output format: raw
            Total usable space: 6.0G
                    Free space: 4.7G (79%)

By the way, interesting virt-builder factoid: It uses a STRIPS-based planner to optimize the order of steps when building the image, so it doesn't waste time doing multiple copies. https://en.wikipedia.org/wiki/Stanford_Research_Institute_Pr... https://github.com/rwmjones/guestfs-tools/blob/0cffcbb7848af... https://github.com/libguestfs/libguestfs-common/blob/74bc5c5... https://github.com/libguestfs/libguestfs-common/blob/74bc5c5...