[Fix] Respect DST boundaries

[jugglinmike]

Account for daylight savings time when calculating whole-day offsets in Date values, and honor the original hour offset in all cases.

• When the offset transitions into daylight savings time, the actual calculation should add one fewer hours to the input time.
• When the offset transitions out of daylight savings time, the actual calculation should effectively add one additional hour to the input time.

Additionally, update the UI to re-use this logic consistently.

[tkellen]

:+1:

[tkellen]

Deployed