Calculate minutes per month from two different date & time values in different months

I want help with excel. I record start date/time and end date/time of an event. And I want to see, for how many minutes that event happens each month.

The problem is, if the start date is at the end of the month and end date is at end of first week of next month, then how do I account for the hours in each month.

Eg Start date & time = 30 july 2012 & 10pm
End date & time = 6 Aug 2012 & 11am


Start date & time = 28 Aug 2012 & 1 am
End date & time = 1 Sep 2012 & 5am


Start date & time = 29 Sep 2012 & 6pm
End date & time = 5 Nov 2012 & 11am


Start date & time = 10 Dec 2012 & 9pm
End date & time = 2 Feb 2013 & 1 pm



I want to work out a formula which looks at the dates and calculates ‘total minutes for the event’ for every month.

The sheet can look like
Jan = __ hours
Feb = __ hours
Mar = ____ hours


thanks

The first month's minutes can be calculated with

=(IF(MONTH(A3)>MONTH(A2),INT(A3-DAY(A3))+1,A3)-A2)*24*60

and assuming that is in B2, the other month is

=(A3-A2)*24*60-B2

Adapt that for your spreasdheet.