Bridget, RM depends on each individual,but once the heart stops,along with brain impulses,the bodys' internal organs,particularly intestines start to break down,and the gases that permeate internally quickly spread. This is why,when someone dies at home,or in hospital even,their bodies are removed within the hour before RM sets in.
3 to 4 hours,and you'd smell the gases. Nowhere have I read that there was a strong smell coming from inside that house.