I've had an app on phone for years, GasBuddy. I use it to decide when and where to fill up. When we travel I decide where to make fuel stops based on price.
I've noticed that gas prices in our area are lowest from Friday to Sunday, then see a jump Monday morning by as much of $0.50 per gallon. By Wednesday if will decline by about $0.25 with the weekend cycle repeated. Call me cynical but I see this as nothing more than a profit manipulation. Those same stations have a fuel delivery about once a week.