Yeah, it surprised me that the water evaporates so quickly. But, it looks like the norm for the ATO to turn on every half hour or so.
When I first set the ATO up I noticed that after it turned off it would continue to siphon water from the container into the sump so I had to raise the tubing up to break the siphon. But in doing that it would sound like someone peeing into the sump when it turned on. I since fixed that, so now it's nice and quite.