One factor to consider is how fast the fertilizer breaks down into a form that the plant roots can make use of. One thing about "organic" fertilizers is that they must first break down via soil bacteria, fungus, earthworms...so timing would be effective if you knew how fast the nutrients make their conversion--or if you used an instantly available chemical fertilizer--maybe foliage feed--if you believe in foliar feeding...

A study done by the UC agricultural division found that roses have their maximum need for nutrients when they are in full bloom. This study was done in greenhouse conditions with the roses in a hydroponic solution. The amount of fertilizer absorption was precisely measured by seeing how much fertilizer was removed from the hydroponic solution by the plant roots, allowing for degradation, evaporation, ect. So giving roses a quick acting fertilizer at full bloom might give you maximum results.

However, simply providing moderate, steady amounts of nutrients in the form of compost and regularly applied organic fertilizers will likely do just as well. Experiment and see what works for you.

Thank you hoovb for the sensible advice.