Thanks for your help, everyone!
As you know, we’re working on improving our ability to handle large engraves. When we say your engrave is large - we really mean that it will take a long time to print. When your Glowforge prints an engrave, the head moves back and forth, line by line, like a inkjet printer. If the design is physically large or if you set your print to have a high LPI, the print will take longer, because the head needs to move further to finish the print. I don’t have exact numbers on size or print time for you, but I hope that helps a little.
Since I can’t give any advice on manual settings, I’m moving this topic to the Beyond the Manual section of the community in case you’d like to continue seeking help there. Note however that advice in this section is unsupported and is not reviewed by Glowforge.