Hello,
Because some systems are slower and others faster … Is safer to let that script run as much is needed for different systems. On my bare metal takes less than 5 seconds and my system is not that fast. On VirtualBox it takes less than that with VBoxSVGA.
Live media and installation works fine in the testing environment (bare metal and VirtualBox) the Manjaro team tested those ISOs on.
Try to collect more information, boot the live system verbose mode and by disabling TLP service …