* In left-to-right languages such as English, check boxes (such as those in the Preference dialog) are supposed to be to the left of the label, not the right, and vice-versa for right-to-left languages.
I did it that way just because of the layout of the rest of the dialog which has descriptions on the left, interactive widgets on the right. I could switch it, but I feel it wouldn't look right...
I think I generally used default layout for checkboxes elsewhere in the app (I let QCheckbox decide for me, probably based on locale). If I didn't, please point it out to me.
* The default date format (%Y-%b-%d %I:%M%p) isn't my system default date format (ISO 8601), and isn't even a standard date format used anywhere in the world. Where'd this weird date format come from? Also, for the example date, it's generally recommended for the time to be after 12:59 PM, to make it easier to differentiate between 12- and 24-hour time.
Ack! I forgot that the date displays differently depending on your time-zone. On
my system the datetime is 10:32pm so that when the user switches to 24hr clock it is apparent. I selected the unixtime to use based on my clock, forgetting others would see a different time. I guess I can manually set the datetime object, to guarantee that the example time shown is 10:32pm on the user's system.
As for default format, you're right. I picked a default I like. And that's why I made it an option. I kind of wanted to use %c for the reason you mentioned, but then it would not be obvious to the user how to modify that field.
* It looks like I didn't fully test the light-on-dark colour scheme handling earlier: unconfirmed transactions in the ledger are displayed in black on a dark background. I understand reducing the contrast for unconfirmed transactions, but I think you overdid it slightly.
I'll see if I can improve that. I set my offline system to a dark theme so that I have a place to test those colors, but obviously it won't be displaying zero-conf tx...