My understanding is that "controlled release" fertilizers work based on moisture and temperatures in the soil. They are coated with a moisture sensitive membrane, which releases the nutrient when the temperature is within a specific range.
From a "greenhouse" related magazine: "Once the CRF prill has absorbed water, soil temperature determines the release rate of nutrients. Depending on the product, the ideal release temperature (i.e., the temperature used to predict the duration of the fertilizer release) can vary from 70°F to 78°F (21°C to 25°C). For example, one type of CRF has an ideal release temperature of 70°F. For a fertilizer with a six-month release rate, 90 to 95 percent of the nitrogen fertilizer contained in the prills will be released over six months if the temperature of the medium is maintained at an average of 70°F."
"...Slow-release fertilizers (SRF)s differ from controlled-release fertilizers in one important way. The release of nutrients from slow-release fertilizers are dependent on multiple factors, not just a single factor like media temperature. Therefore, the nutrient release from SRFs is less predictable than from controlled-release fertilizers."
That's great info, Bro!
Just to add to it...My understanding is that the release rate for all CR fert's is based on a 70*F ambient temperature and for every 16*F increase, the release rate doubles. This means, if your ambient temp goes from 70*F to 86*F, the six-month release rate is reduced to 3 months. In other words, if it's warmer than 70*F, you'll need to re-fert sooner.