My understanding is that it is not very fast. I had taken notes about this but now I can't find the exact numbers.
If I remember correctly trading $100 in $1 chunks would take a hour or two. You would have to increase the chunk size to speed up trading, but that introduces more risk.
Note that subatomic swap technology is totally different from atomic swap technology. With atomic swap technology the trade speed depends on blockchain confirmation times and not on the trade volume.