If it takes longer than 20 minutes for the roots to get water, the roots will usually grow long, And they can grow very long looking for the nutrient solution source.
In fact they can grow so long and thick that they prevent the solution from reaching all the way up your grow cups. This will also raise the chance of root material being ripped out and clogging the system. Once the flow is clogged by root or other material inside, you will have to take the garden apart and clean it.
Check the root length every few weeks. If it is hard to remove the cups the plants are in because the roots are anchored to the internal channel, the roots are too long. The root should be short enough to not touch the narrow point where the solution enters the cup holder. If they are too long, trim them down with scissors. Make sure they are not going too far, but don't cut unnecessarily.
