Refine start/end times when set to 00:00; create 4th import

Start time of 0000 changed to 1200; end date (when present) time
changed from 0000 to 1300. This avoids having a time of “7pm-7pm”. Not
a perfect fix, but an improvement. Many old events simply don’t have
times. Short of applying a rule that will need to be applied forever,
(despite the problem being fixed for newer events), this is the best
fix.