Yeah it only lasts 24 hours, and the next day you can just do it again... However sometimes it's cloudy and you can't really see the sun, so it's hard to determine where to shoot.
I've used the time of day to kinda get an idea of where it would be in the sky and have been very successful with this. The sun seems to move directly over top of you as well. Unlike how, on earth it moves at an angle and that will vary depending on the season and all that jazz. It makes it pretty easy to figure out approximately where it is. And mabye I'm just that good

but it seems like you don't really have to hit it dead on. Like, hitting the general area around the sun seems to work. At least that's what I'm assuming because I don't think I've ever missed the dang thing, even on cloudy days. And I find it hard to believe that I hit it dead on everytime.