What about creating a little widget on Skydemon for keeping tabs of fuel tank switching times and also reminding you when it's time to switch. So you can customise the timer, e.g. 15/30 mins etc. Then on the widget, you select left or right fuel tank then it automatically starts your timer, after x amount of time it pops up with a reminder to switch tanks. You can then switch tanks on the widget and it restarts the timer.