Of the five most common bacteriophages that live in the dirt in my part of the country, though they are all genetically quite different, all of them fall into the same general bucket as far as what temperature to use, and for what length of time. The capsomers will begin to denature at temperatures above 50-60°C (122-140°F) and can fully denature at temperatures above 70-80°C (158-176°F). The timescale is in minutes. That is about as specific an answer as I can get after extensive googling. All I can do now is collect samples, create lawns on TSA plates, isolate strains, pick plaques if and when they appear, denature the plaques at different times and temperatures within the parameters mentioned above, and test to see exactly when and at what temperature the cooked plaques fail to inoculate other colonies.