Too much water or not enough?
Leaves Turn Yellow
Certified GKH Gardening Expert
Yellowing leaves does generally mean a watering issue. To much or to little as you indicate.
You do need to check the soil, by touching the just below the soil surface, an inch or so down.
Make sure the pot is well draining, and water is not pooling in the soil.
Also if the temperatures are about 85 degrees you will most likely need to water twice a day.
There can be other reasons for hibiscus leaves yellowing.
You can check the link I have provided.