SUMMARY
The new interface to change custom times when night and day colors begin feels a bit weird. I asked a few different friends and family members and here I summarize some ideas to improve it.

First, the top bar looks super good and it's the first thing the user tries to use. However, as it is, it only shows information, but it is not interactive. Why not allow the user to drag the limits there directly to change the custom times? If this is possible, perhaps it is even okay to remove the time fields below.

Hour numbers in the bar look also a bit weird, specially the zero. Why not 24 so it's clear? Or 00, 01, 02, etc.? Or use the locale settings and use 24h or 12 am/pm format. The am/pm text can be shown on top of there is no space together with the numbers

Finally, in the two fields to change the time, the first thing all users try to do is to delete the numbers, but this is not possible. I think at least, the delete key should move the position to the left. The user has to use the arrow or click at the beginning of the number to introduce the time. I think these fields should be more intuitive and feel more responsive. Probably this is not a thing to improve here but on Qt or Frameworks.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.93.0
KDE Frameworks Version: 5.249.0
Qt Version: 6.7.0
Kernel Version: 6.7.4-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 8 × 11th Gen Intel® Core™ i5-1135G7 @ 2.40GHz
Memory: 15.3 GiB of RAM
Graphics Processor: Mesa Intel® Xe Graphics
Manufacturer: LENOVO
Product Name: 20XYCTO1WW
System Version: ThinkPad X1 Yoga Gen 6