Solved using this approach:
var start_t = 0;
var end_t = 0;
var point = event.point;
var points = event.point.series.points;
var index = points.indexOf(point);
var index_next = index+1;
start_t = point.x;
if(index_next==points.length)
{
index_next=points.length-1;
end_t = points[points.length - 1].x;
}
else
{
//Is not the last
var next_point = points[index_next]
end_t = next_point.x;
}
var period =
{
from: start_t,
to: end_t
};
...