The third option might be a middle ground: +0:30, though I guess a lot of timezone dropdown boxes would suddenly break at that one (not that they worked to begin with).
There are plenty of places that already offset by half an hour (Newfoundland for example) or even a quarter of an hour (Chatham Islands in New Zealand) so any dropdowns should already handle this.
Sadly, a lot of dropdowns I encounter handle only even offsets from -12 to 12... The state of modern web forms is sad.