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.
The file format is also the message format to the GUI. I'd rather use ints if I can get the GUI to play along. Please config an around time and change it in your working setup to see what I mean. Using formatted time strings was the only option I found around this issue.