I’ve read on multiple sources that you should use incense when you have no sightings on your radar, this was false. Do not waste incense if someone tells you to do this.
When you should use incense? You know you are walking around, if you are staying put you won’t get the full benefits of incense (if you stay put you’ll see a Pokemon show up every 10 minutes). When walking around you’ll see more Pokemon are lured your way.
When you should NOT use incense? Driving… You’ll see new Pokemon appear, but when you try to catch them you will notice they “run away”. I couldn’t catch a single Pokemon while I was in the car, I believe it has to do with the distance traveled when you are in a vehicle. This only happens when I use incense.
There is no “secret” timing of when you should use incense, it is more so of knowing you can roam around then use your incense. Do not waste it…