Advanced Preferences can't handle "24:00"

[Didactylos]

Advanced Preferences can't handle the value "24:00". Neither can the simple prefs, but that doesn't matter since "Never" isn't a useful value unless you can override it with the per-day settings.

(This is almost-but-not-quite a duplicate of #300)

But this is just another bug in the advanced preferences. If it were my call, I'd bump the entire advanced preferences dialog to 6.0.

Also see #351, #352 and #173.

[Nicolas]

_{Just a sidenote: you can link to the advanced_preferences tag to see all the related tickets.}