Code miners revealed an interesting fact. If you are sitting on the couch and using Incense for 30 minutes, a Pokemon will appear every 5 minutes. HOWEVER if you walk for at least 200 meters, a Pokemon will appear every minute.
I am really disappointed so far by the Pokemons that spawn near me using Incense. I’ve noticed the 5 minute rule isn’t very accurate.
The code says that people who stand still will find a Pokemon every 300 seconds. People who are moving, though, will find Pokemon every 60 seconds. The distance you need to travel to find Pokemon more quickly is 200 meters (.2 kilometers).