Light bulb moment
(its amazing what a hot shower can do for brain function
). Plants respirate through their leaves as part of the chemical reaction of photosynthesis. Some plants repirate during the day, but most at night. But, if the process of resiration is faster than the plant can absorb water (or if there's not enough water), they wilt.
As your plants are in plastic pots, you can feel when they need water by weight. Lift them right after you water. Lift them before you water (when you know they are dry). Feel the difference?
Yes, water until some flows out the bottom but, don't let them sit in water. Don't fertilize.