Swing speed depends on plant size, numbers, light wattage and nutrient solution volume. The easiest way to increase swing time is to use a larger volume of solution, with a smaller volume of solution increasing the speed. Without hitting the lower 5.3-4 range of the pH swing, your plants are not getting the full absorption of all elements properly. When you work this into your method, you'll see a lowered need for nutrient strength and a higher end quality.
I use r/o, like I described. The pH swing is completely different, it rises as the plants use the nutrients. I don't do res changes at all, not until 5 days before harvest and that's only to switch out the nutrient solution for pure r/o, non-pH'd. The pH is rock solid and predictable in how long it takes to rise. Unless you're using r/o, I really have no idea how to advise you on your situation. It's one of the key reasons I also strongly recommend r/o, the pH works the same way for everyone.