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.
I still don't like the idea that 0 (which is a perfectly valid minutes from midnight) is used as the not set value. -1 would be a much better value.

So this sounds like you've kept hte old bug and that I cannot use midnight as a value, this is wrong.