Hey there,
Dealing with fungus gnats can be a real nuisance, but using Diatomaceous Earth (DE) is a good step towards controlling them. It's great to hear that it's working to some extent, but it's not uncommon for it to take some time to completely eliminate the problem.
Your approach of watering in the morning and applying DE by noon is a good strategy. DE works by dehydrating and ultimately killing the insects that come into contact with it, so it needs time to take effect.
Typically, it may take a couple of weeks to see a significant reduction in the fungus gnat population, especially if they're already established in your grow space. Keep up with your current routine of watering and applying DE, and be patient. Over time, you should notice fewer and fewer fungus gnats as the population diminishes.
In addition to DE, consider other methods to tackle the issue, such as improving drainage in your soil, allowing the top layer of soil to dry out between waterings, and using sticky traps to catch adult fungus gnats.
With consistent effort and patience, you should be able to get the fungus gnat problem under control. Hang in there, and keep up the good work!
Happy growing! π±