How could I measure the hours of light in a day? And how can I make a plan?

Maybe there's an app for that? Some kind of time lapse app? Or maybe set up a magnifying glass or a crystal ball on a stand and a piece of paper under it. As the sun passes, it will might burn a line on the page. As to how you would read this line, you would need some kind of measurement system - maybe do a baseline the day before and use you watch to record start and finish times.