There is ZERO reason to use VBR encoding, slows down the process and when you have such a short program CBR will be a ton faster and in most cases it will be better. Set the CBR bitrate to 7Mbps and let her rip, if should be close to real time, even if you are sending it from the FCP timeline, but Exporting it will speed up the encoding process but CBR will be even a bigger improvement.