Changed aroundtime to a time window (feature #1400)

@ProfYaffle & @adamsutton I rebased and cleaned up my version of the patch as discussed in the old pull request.
How does a return of 0 if not found work vs finding midnight? Don't they both return zero? Is that a problem anywhere? (it may not be if values are only ever entered via the combobox, so the time should always be found and be valid)