I only read a couple, but from what I can tell from that damned Stargate wiki's liberal understanding of the word "canon," they seemed to have a problem with "the past all happened at the same time." Something I read just recently said they established Janus invented the time loop machine. Janus, who was part of the last generation born on Atlantis that abandoned it ten thousand years ago, built the timeloop machine intended to prevent the plague that led to Atlantis fleeing the Milky Way, ten million years ago. It's especially irritating to me because I'm actually quite interested in the concept of a civilization whose history is measured in eons, where great founders and inventors and achievements and infrastructure they use daily were are as old as the dinosaurs are for us, if not the very mountains. Or we can just say Time Travel Guy must've done all the Time Travel Things we ever heard of.