I have recorded the sunrise at 6:00 and the sunset at 14:30 with a duration of 240, but there is a phenomenon that a sunset image appears at 9:30 in the morning. What's the reason?

There are actually only three pictures used in this background, the sunrise and the sunset background are the same image. Unfortunately the artist that made these backgrounds never made a fourth image :(

Does this answer your question, or is there another issue where an image is flashing at 9:30?

I would love to more of these wallpapers in the future, but art is not really my forte. So, if you know of any other image sets that could be used to represent a time of day cycle please do let me know!

That's not it, I change the setting
Sunrise 06:00
Sunset 14:30
Duration 240
I used it for a few days. Sunset images appear around 07:00 am ~9:00am. The duration seems to affect the sunrise. It would be more efficient to set the night time time rather than adjusting the sunset time by duration.

OH! Yeah the duration time sets the duration that the sunset/sunrise image is displayed after the sunrise or sunset time has been reached.

Example 1
-----------------------
Sunrise 6:00
Duration 240

The sunrise image will then be displayed from 6:00 to 10:00 am since 240 mins = 4 hours. At 10:01 am the background will then change to the daytime image.

Example 2
-----------------------
Sunset 14:30
Duration 240

Again the duration is 240 mins/4 hours, so the sunset image should be displayed from 14:30 to 18:30 or 6:30 pm. At 6:31 pm the background should change to the night time image.

I hope this helps to clear up any ambiguities in the values for sunrise/sunset times and the duration value.

Hey, could you possibly make it so we can change the position vertically/horizontally? Also, if possible, could you make it so we can center the clock?

Hey cap'n! I mentioned some stuff about this in the main comments for the wallpaper just now. Cheers!