What is the difference between 60 nights & 90 nights Allout Mosquito repellent refill? Though quantity is same?

The difference is either they (manufacturer) have a difference in the concentration of the repellent, OR are giving you a smaller ';dose'; per use.What is the difference between 60 nights %26amp; 90 nights Allout Mosquito repellent refill? Though quantity is same?
Please check the quantity is not the same.