Kraken: fix overlapping of two stop_times of a vehicle_journey

It could happen that we have 2 stop_time at vj looking alike:
ST1: arrival_time:   8h00
     departure_time: 8h10
ST2: arrival_time: 8h05
     departure_time: 8h15
It can happen at the first vj.

With the previous method, when we marked ST1, we were retrieving ST2.
AND THAT'S NO GOOD!
should be second_per_day no ?