I waited for 15 minutes. Does it take half an hour to install each time? It doesn't take as long when I fastboot and install or even Just boot cyanomod recovery and install miui rom from that.... Looks to me there is an Error in install routine with twrpYou just have to let it continue with the installation. It's running on background. I had exactly the same problem since the devs included TWRP in the new releases but the installation works perfectly.
You have to wait several minutes, it will reboot and the install will continue on the Miui logo with the 3 dots.