How can I display a cell of 2 hours and also how can i change the text of left nav from one hour slot to half hour

At this moment neither is possible:

1) The maximum cell size is 1 hour (CellsPerHour="1").
2) The size of the headers on the left side is always one hour and the text is generated automatically from the hour name (you can only change the 12/24 time format).

I expect both will be made available after the next DayPilotCalendar rewrite (the limits are internal). I expect it will be rewritten in a 6 months time frame.