|C1 ends up 23:35 not 0:25 that it should be.|
NO, the formula is correct. The time difference between:
12/05/2011 12:15 AM and 12/05/2011 11:50 PM = 23 hours 35 minutes.
Do you really mean that the times should be:
12/05/2011 11:50 PM and 12/06/2011 12:15 AM
You have gone past midnight into the next day.
Try this formula: