Generally, it will take two weeks to see the effects of the treatment, and the effect lasts three to six months. Over time, you may require fewer treatments because weaker muscles atrophy and require fewer injections.
The hibiscus is a heavy feeder that prefers frequent but light fertilizing. A nitrogen fertilizer in the spring and a high potassium fertilizer in the summer work well for the hibiscus plant. Also, fertilizing at the beginning and during the growing season gives the hibiscus needed nutrients for growth.
I have used them on both tropical and hardy hibiscus and the gardenias. I have taken to incorporating them into my potting mix for other plants this year and I have been seeing far fewer bugs. However, this may be just because the soil is amended and the plant grows healthier.