At this moment the scheduler only works with .startDate and .days properties.
You can use DayPilot.DateUtil.daysDiff(first, second) helper method to calculate the .days property:
var days = DayPilot.DateUtil.daysDiff("2015-10-01", "2015-10-03");
It accepts DayPilot.Date objects and strings in ISO 8601 format ("2015-10-03", "2015-10-03T14:00:00".