If I'm following your workflow, ProRes LT exporting to YouTube, you're not transcoding again to ProRes you're simply exporting from the timeline a YouTube fashioned encode, correct? So what you're exporting is H.264, probably 720p. That's your 1st bottleneck, H.264 encoding is s_l_o_w. The 2nd bottleneck, uploading to YouTube from the desktop is really dependent on the bandwidth you're getting at the prescribed time. Sure, lower the necessary bandwidth by encoding out an H.264 video, 854x480, at something like 1200-2000 kbps (SD Video Sharing) and it's going to upload faster to YouTube but YouTube is sort of a crap shoot sometimes. Prime-time YouTube traffic is high so avoid that. You can also upload directly to YouTube on the encode via Compressor and you don't have to sit around for the extra step from your desktop.